Chasing down a poor idle problem. Tests indicate a vacuum leak at a couple of spots on the carb. One of them is at the idle by-pass screw. They provide air at idle that is "variable" as that screw is adjustable. I believe it adjusts air that passes through a passage inside the carburetor. I am not sure if that passage air is obtained externally, past the screw, OR fed internally from inside the carb.
Does anyone know of a "fix" for these idle by-pass screws once they are leaking air, and a source of a vacuum leak? If the air feed is NOT external, so unwanted air flows past the idle by-pass screw, would a rubber O-Ring work? If the feed is internal what can be done? I imagine a clogged passage might force air in past the screw as a path of least resistance, thus grabbing air externally? Any thoughts? Thanks. Clay/Lexi
Quote from: Lexi on August 23, 2024, 09:22:47 AMChasing down a poor idle problem. Tests indicate a vacuum leak at a couple of spots on the carb. One of them is at the idle by-pass screw. They provide air at idle that is "variable" as that screw is adjustable. I believe it adjusts air that passes through a passage inside the carburetor. I am not sure if that passage air is obtained externally, past the screw, OR fed internally from inside the carb.
Does anyone know of a "fix" for these idle by-pass screws once they are leaking air, and a source of a vacuum leak? If the air feed is NOT external, so unwanted air flows past the idle by-pass screw, would a rubber O-Ring work? If the feed is internal what can be done? I imagine a clogged passage might force air in past the screw as a path of least resistance, thus grabbing air externally? Any thoughts? Thanks. Clay/Lexi
@Clay,
Not sure if you have the full Rochester 1956 Cadillac Service Training manual, here is the section discussing the idle-bypass section, this may be of help on your topic.
Let me know if you want the full copy (large file) so I'll be glad to send it over via email.
Quote from: J. Gomez on August 23, 2024, 06:29:21 PM@Clay,
Not sure if you have the full Rochester 1956 Cadillac Service Training manual, here is the section discussing the idle-bypass section, this may be of help on your topic.
Let me know if you want the full copy (large file) so I'll be glad to send it over via email.
Jose, much thanks! I do have that Rochester training booklet. It helps a bit, but fails us at critical points as it shows adjustment set up when all was new. Does not delve into trouble shooting or how to fix 70 year old worn parts. Update on our phone call; I only got to look at the car a day or so ago and carb vacuum leaks appear to be the problem. Just not sure what rebuilders do with one of those idle by-pass screws if it is at fault. As we discussed they are notorious for not working properly or at all. As Fishnjim once said a way back in this Forum, that was a "
terrible" system. Well its come back to haunt me and not sure what to do. Digging through my parts and hope that I can cobble something together. Might try an O-Ring and/or if there is a spring there, look for a stronger one or increase it's tension with a couple of washers. Clay/Lexi
Without knowing what tests you made, what follows may be repetitive. Ag=after closing both of the idle jets and then opening them to the base setting of 1 1/2 turns +/- does the engine run and if so how. If you turn the crews all the way in does the engine stall. Does opening them past the base affect the idle rpm or the smoothness of the engine?
Did you spray starting fluid, Brakleen, hair spray etc. around the base of the carb and especially around the throttle shaft to see if the idle smoothes or the rpm increases. Best to use the aerosol cans with a snorkel tube on and the air cleaner installed. That will help avoid a false positive.
My thought is the leakage may be around the throttle shaft followed by the base gasket or a slightly deformed carb base, the latter easily cured with a flat plate or glass and emery cloth. Obviously if the gasket is cracked , deformed, etc. replace it.
I don't remember if the 56s have an insulation block under the carb, but if so. remove the carb and check the block for cracks.
tony
Quote from: tcom2027 on August 23, 2024, 08:51:21 PMWithout knowing what tests you made, what follows may be repetitive. Ag=after closing both of the idle jets and then opening them to the base setting of 1 1/2 turns +/- does the engine run and if so how. If you turn the crews all the way in does the engine stall. Does opening them past the base affect the idle rpm or the smoothness of the engine?
Did you spray starting fluid, Brakleen, hair spray etc. around the base of the carb and especially around the throttle shaft to see if the idle smoothes or the rpm increases. Best to use the aerosol cans with a snorkel tube on and the air cleaner installed. That will help avoid a false positive.
My thought is the leakage may be around the throttle shaft followed by the base gasket or a slightly deformed carb base, the latter easily cured with a flat plate or glass and emery cloth. Obviously if the gasket is cracked , deformed, etc. replace it.
I don't remember if the 56s have an insulation block under the carb, but if so. remove the carb and check the block for cracks.
tony
Hey Tony, thanks for chiming in. My test time was very limited, but I did spray brake clean around the base of the carburetor and at a few other areas of interest. The air cleaner was in place during testing. When brake clean hit the idle by-pass screw, engine RPMs jumped quite noticeably. Engine RPMs jumped even more when in contact with the secondary throttle shaft, (but not reactive with the primary throttle shaft). Covering the carburetor with a gloved hand also noticeably increased the engine RPMs, rather than stalling the engine. The '56 has no insulator base gasket, just a regular gasket. When sprayed, that area seemed fine. My testing will continue. Wish I knew more about that idle by-pass screw. It would make sense for perhaps some vacuum leakage, but not what I experienced, in my opinion. On a side note, I got a nasty shock from #1 spark plug wire, so must be a break down in the insulation there. So I installed another wire, but that had no noticeable impact on the idle. Clay/Lexi
Quote from: Lexi on August 23, 2024, 08:35:09 PMJose, much thanks! I do have that Rochester training booklet. It helps a bit, but fails us at critical points as it shows adjustment set up when all was new. Does not delve into trouble shooting or how to fix 70 year old worn parts. Update on our phone call; I only got to look at the car a day or so ago and carb vacuum leaks appear to be the problem. Just not sure what rebuilders do with one of those idle by-pass screws if it is at fault. As we discussed they are notorious for not working properly or at all. As Fishnjim once said a way back in this Forum, that was a "terrible" system. Well its come back to haunt me and not sure what to do. Digging through my parts and hope that I can cobble something together. Might try an O-Ring and/or if there is a spring there, look for a stronger one or increase it's tension with a couple of washers. Clay/Lexi
Clay,
Agree that document is more of an operation theory than a troubleshooting guide, and even the Service Manual does not provides enough details for troubleshooting.
There should be a very limited vacuum leak at the adjustment screw as the spring would provide tension against the threads to seal depending on how far the screw is out. If the screw has to much play it may not provide the proper sealing.
Agree, you can try adding an "O" ring and a flat washer at the end of the screw and sandwich them against the spring and see if that helps.
Good morning,
Strange that the threads are worn or the seats in the carb are damaged to the point you have a significant leak. I assume you took a close look at the tips of the needles. They or the seats may be damaged from over tightening.
How does the car run with the needles turned all the way in to the stops?
The throttle shaft and the idle screws are going to leak a little even when new, more as they wear but that is compensated for in the design of the carb.
This may be a bit afield but have you checked all the vacuum hoses, particularly the ends where they attach to a vacuum operated component? Nip off the ends to get a tight fit. The brake booster can have sneaky leaks. Same for a vacuum hose that got pinched or laid against the exhaust manifold a long time ago and finally died.
THere are guys here that know more about the Rochesters than I do. Remember it ran well .....until it didn't, so the problem can be corrected. To loosely (very) quote Sherlock Holmes, "When all the other possibilities, however impossible or improbable have been eliminated only the truth remains."
tony
Quote from: J. Gomez on August 24, 2024, 10:21:13 AMClay,
Agree that document is more of an operation theory than a troubleshooting guide, and even the Service Manual does not provides enough details for troubleshooting.
There should be a very limited vacuum leak at the adjustment screw as the spring would provide tension against the threads to seal depending on how far the screw is out. If the screw has to much play it may not provide the proper sealing.
Agree, you can try adding an "O" ring and a flat washer at the end of the screw and sandwich them against the spring and see if that helps.
I agree. A process I will have to investigate Jose. I assume that the air which the by-pass screw is regulating is internally fed, and is first filtered through the air cleaner. Why pull dirty air into the engine and by-pass the air cleaner? I agree that there would probably be some leakage there, but in my case it seems extreme. Clay/Lexi
Quote from: tcom2027 on August 24, 2024, 11:26:32 AMGood morning,
Strange that the threads are worn or the seats in the carb are damaged to the point you have a significant leak. I assume you took a close look at the tips of the needles. They or the seats may be damaged from over tightening.
How does the car run with the needles turned all the way in to the stops?
The throttle shaft and the idle screws are going to leak a little even when new, more as they wear but that is compensated for in the design of the carb.
This may be a bit afield but have you checked all the vacuum hoses, particularly the ends where they attach to a vacuum operated component? Nip off the ends to get a tight fit. The brake booster can have sneaky leaks. Same for a vacuum hose that got pinched or laid against the exhaust manifold a long time ago and finally died.
THere are guys here that know more about the Rochesters than I do. Remember it ran well .....until it didn't, so the problem can be corrected. To loosely (very) quote Sherlock Holmes, "When all the other possibilities, however impossible or improbable have been eliminated only the truth remains."
tony
I have not had the time to conduct all the tests that I would like to. In some instances I am not sure that my physical examination would even be revealing. I am not a "carburetor" guy, and am not qualified to evaluate the condition of some parts. The idle by-pass screw is also a long abandoned technology that even niche specialty rebuilders might be unfamiliar or uncomfortable with. Most present day mechanics at least up here, have never even worked on a carbureted car. Quick tests seemed to reveal the other vacuum connections were good. Good point, the car ran well the day before so I am hoping it can be corrected in a reasonable manner. All I know now is that when sprayed with Brake clean at those 2 carb spots, the RPMs jumped significantly, which I understand is indicative of a problem. There could be other gremlins lurking about as well. Hope to get back at it this week. Clay/Lexi
Quote from: Lexi on August 23, 2024, 08:35:09 PMJose, much thanks! I do have that Rochester training booklet. It helps a bit, but fails us at critical points as it shows adjustment set up when all was new. Does not delve into trouble shooting or how to fix 70 year old worn parts. Update on our phone call; I only got to look at the car a day or so ago and carb vacuum leaks appear to be the problem. Just not sure what rebuilders do with one of those idle by-pass screws if it is at fault. As we discussed they are notorious for not working properly or at all. As Fishnjim once said a way back in this Forum, that was a "terrible" system. Well its come back to haunt me and not sure what to do. Digging through my parts and hope that I can cobble something together. Might try an O-Ring and/or if there is a spring there, look for a stronger one or increase it's tension with a couple of washers. Clay/Lexi
Clay/Lexi - I believe the spring is there to prevent the adjustment from turning. The screw should have a tapered end. I've never heard of them "leaking." I would suspect a failing mounting gasket.
For the idle screws to be effective, the throttle plates must be sealed to the carb bores, otherwise, air can be drawn in there and they will never be adjusted correctly. Also, you found the throttle shafts leaking, same issue, too much air being allowed in. The internal orifice in the carb is tiny for the idle circuit, so a good soaking, cleaning, thin wire to feed through to make sure nothing is blocking the passage way, compressed air to blow out will be needed. I have a Rochester carb book and can take a photo of the info there.
"For the idle screws to be effective, the throttle plates must be sealed to the carb bores, otherwise, air can be drawn in there and they will never be adjusted correctly. Also, you found the throttle shafts leaking, same issue, too much air being allowed in. The internal orifice in the carb is tiny for the idle circuit, so a good soaking, cleaning, thin wire to feed through to make sure nothing is blocking the passage way, compressed air to blow out will be needed. I have a Rochester carb book and can take a photo of the info there. "
COMPRESSED AIR!!!! Gum Out usually can not blow out fuel separation, aka brown gunk that settles, gets heated up and bakes into these tiny passages at the super heated base of the carburetor.
About 4 years ago this carb was reportedly leaking air at both throttle shafts as well as the idle by-pass screw, by my local mechanic. I had it rebuilt and saw it running on the engine test stand prior to taking it home for installation. It ran fine and I seem to recall that the rebuilder sprayed it while running and RPMs were not significantly affected, if at all. He did not have to re-bush the throttle shafts, as it was determined that there was "gunk" inside presumed key passages. So a good cleaning as James suggested is what fixed it before. The rebuilder also advised that many classic car owners come in wanting a throttle bushing job, which usually isn't required, he said.
This time, 4 years later, just the idle by-pass screw and secondary throttle shaft is leaking, (and not the primary). Noteworthy, is that after running 7 minutes the car will idle without me having to nurse the accelerator pedal, (but still not 100%). Seems that enough heat build up after 7 minutes may be partially swelling a key air leaky area, thereby causing a partial seal at the source of the leak.
As my car makes many local short trips, it seems reasonable to perhaps blame the carbon/gunk build up on these driving habits. Even though I often try and incorporate a (very) short highway run, (being mindful of this possibility), perhaps my driving habits are still insufficient, and causing this issue?
Happened with the carburetor prior to this one. Again, it needed to be tanked after about 4 years. Same issues with vacuum leaks at these same areas. Seems something to be mindful of for those who drive these older carbureted cars, and that a much longer periodic highway drive is required as preventative maintenance-to keep the "gunk" build up at a miniumum.
Now that these carbs are pushing 70 years of age, and that we are filling our gas tanks with inferior fuel, rebuilt carburetors may not "last" as long. Any thoughts? Clay/Lexi
CLay,
May I respectfully suggest that Lexi needs a long trip during cool weather on a flat highway that is not congested with stop and go traffic with a full tank of high(est) octane gas? Having owned two SDV's during the 60's and 70's, my two engines remarkably perked up after long highway runs. If your vacuum advance is working, and a vacuum gauge indicates a relatively steady 18 inches, then a long ride will likely enhance Lexi's operation... here's what I discovered--- acceleration became more responsive, engine idle smoothed out, exhaust "stacks" turned brown instead of black. The improvement, as I recall, was noticeable. I have absolutely no solid evidence regarding what was going on to improve performance, but I am certain these engines do not run well if they're doing short, around town trips. Benefits of electronic technology introduced forty years ago include electronic engine management systems that our older models engines don't have. I also recall that the exhaust heat riser tended to get stuck, and the exhaust passages under the carburetor tended to plug up. Hope this helps, James
Makes sense to me James. Lexi did make a long highway trip last August, but none this year. She has made a lot of short highway trips like 10 or 20 minutes each. When doing these short runs I usually try to take her out on the highway even if for a bit, to avoid what you describe. As I noted in my last post, those may not be enough. Living around the Greater Toronto area is brutal as traffic is terrible, some 50 miles in either direction. Its an odyssey just to get far enough away to avoid the congestion. But even after those short runs she did seem to run better. Oddly enough, the day before her problems surfaced, I had her out on the highway for about a half hour. She has no heat riser valve. Too much life getting in the way lately, so hoping to get back to look into this problem soon before the driving season is done. One question though James, why a long drive in "cool" weather? Clay/Lexi
Ok, you are going to think this is absolutely crazy, but here goes--
What about covering every external hole that doesn't need to move (such as the throttle shaft) with something to see if it helps at all.
I don't know if some sort of tape would stick, but how about--I can't believe I am even going to say this-- sticking something like a wad of chewing gum over things like idle screws, etc. You are going to rebuild it anyway so it will get clean. Doing something like this would tell you if your air leak is internal or external.
I'm sure there's something better than sugar free Trident, but you need something that will form to the openings and be removeable.
I can't believe I suggested chewing gum-Ugh.
How about some plumber's putty?
Maybe screw the idle bypass screws in to the stops and see what happens. If the engine keeps running you can assume the problem is internal or there is a vacuum leak elsewhere.
Quote from: J. Gomez on August 23, 2024, 06:29:21 PM@Clay,
Not sure if you have the full Rochester 1956 Cadillac Service Training manual, here is the section discussing the idle-bypass section, this may be of help on your topic.
Let me know if you want the full copy (large file) so I'll be glad to send it over via email.
Excellent explanation with very clear drawings.
The Idle By-Pass screw is basically a controlled vacuum leak. Not sure what it looks like inside where it is supposed to regulate filtered air I believe already passing into the carb, for curb idle. I am told that for later vehicles that still used them, they got much bigger and tapered, presumeably to better control air flow. On a couple of my carb cores I removed these screws and they were both about 1.5 turns out. Probably the last adjustment when they were last on a running vehicle. At the business end, inside the carburetor where the air idle flow regulation takes place, these ends are cut off flat. Not sure if they mate 180 degrees up against an air passage port or whatever. Upon close examination one of them appears to be more at 90 degrees, (the "flat" part), than the screw from the other core. One appears more "worn" than the other, eyeballing it and also confirmed when I put a watch makers minature brass square on it. Perhaps over torqued at one point by some ham fisted individual? Just like the idle screws up front, not good to over tighten and bottom this idle by-pass screw out? Thinking out loud, I wonder if one repair we could investigate is whether squaring that end to 90 degrees, if off, would better address such problems as I have heard so often that the idle by-pass screw does not even work? Could that be because the end is slightly worn so not as efficient at blocking unwanted air? Will try to get a clear photo, but a tough task as everything is so small and I probably don't have the magnification to show this. Mention this FWIW. Clay/Lexi
Hey Clay,
From what I can recall, those air bleed screws on the carburetor are not drawing air from a filtered source, it pulls directly from the engine bay. That's one reason why they did away with those in later years.
Some of the early 2 barrel Rochesters used to have a slot cut into the gasket between the base plate and the bowl assembly that did basically the same thing but without adjustment.
Shutting down a hot engine would hot soak the fuel in the carb, and the fumes would escape through the vents and wherever there was not a good seal, like throttle shafts and those air bleeds.
Rick
Hello Rick. I took some photos which I will post later. Looks like the "flat end" of the idle by-pass screw does not press up against anything, but it does enter a round port. Clay/Lexi
As it has come up before and will come up again, for future reference here is the idle by-pass screw out of a 1956 Rochester 4GC carburetor from a '56 Cadillac. First shot shows a near pristine example. Second shot shows another with wear near tip. Perhaps a source of leaks if the circumfrence is out of round? May explain why tapered ones followed later. Next shot shows carb upside down with tip of the idle by-pass screw showing in it's passage, and also the round port it enters, (there but dark to see), highlighted by red arrows. Last shot shows same, but where I also inserted a pick to probe the round port that the screw goes into, see red arrows for 1) probe 2) tip of probe and 3) screw flat end. By filtered air I meant air that has passed through the air cleaner. That Rochester booklet says the air comes from the "primary bore". I take it that is the "horn" of the carburetor, so air first passes through the air cleaner to get there. Could have interpreted it wrong though. Will leave that up to the carb experts. But this is the screw that many say they have problems with. Clay/Lexi
I took some photos of the Rochester Carb catalog I have. These pages are for 55 and 56 Rochester carbs, not dual.
Maybe this will assist.
While I do have this same catalog, it is good that you posted these images for reference. Hope to look at my car this coming week. Thanks for helping out. Clay/Lexi
Clay,
This is what I was thinking about when you asked your question. On the early small bore Rochester 2bbl carbs, they did a couple things to vent the fumes after the engine shut down.
Screenshot_20240831-141329_Gallery.jpg
20240831_141517.jpg
This is the back of one with a hole in each side that is just vented to the engine bay. No filter, screen, nothing, so when the engine is running it can draw in air, and dirt, through these.
20240831_135717.jpg
Another method they used was to cut slots in the gasket between the base and body as you can see in the top two gaskets. The bottom one doesn't have any of that.
20240831_135739.jpg
Here's the paperwork from a rebuild kit for one.
You are probably right about that air bleed screw drawing air from inside the air filter.
When I read your question the first thing I thought about was this 2bbl design.
Sorry for the misdirection.
Rick
That makes sense. With the Rochester 4GC, the service training booklet identified drilled holes in the casting also as vapour vent holes. I think if you go back to Jose's posted image file of the diagram, these were in the diagram. Clay/Lexi
Well, I swapped carbs today and had a better look around under the hood. Aside from the secondary throttle shaft and idle by-pass screw vacuum leaks, I found a small chunk missing from my base gasket when I removed the carbureteor. When I had sprayed that area earlier, I also noted a vacuum leak there and I thought it might have come from the idle speed up control valve. They are vacuum connected and have a diaphram in them. With the engine running and the fan blowing the spray back, it was difficult to determine what area had the leak. The idle speed up unit is right where the leaky gasket is. Fortunatly, I had a replacement gasket ready to go. Attached image shows the damaged gasket area. Steel showing through with a portion of the gasket material missing. I have no idea what happened to it. Car now is running but difficult to keep idle down. Idle-by-pass screw not working the best, but at least the car is mobile again. Might have questions regarding idle later on. Clay/Lexi
Note: That damaged area is adjascent to the choke warming area in the intake manifold casting, (blocked in by a previous mechanic). I would think this would not be an area prone to vacuum leaks. Although the gasket looked a little rough, I did not notice any spikes in RPMs when checked, just a tiny rise in this area. Will have to check the idle speed up valve more closely.
Clay,
Just a quick observation here. That missing section on your gasket is in the exhaust channel that runs under the carb. You said the passage is blocked off, so nothing really runs through that section of the gasket, which would include vacuum.
Unless there is another area of the gasket that is missing that connects to an actual vacuum source, the missing section you show should not affect how your engine runs.
Since the exhaust was blocked, you could actually cut away that front section of gasket and it wouldn't cause any issues, except for maybe not supporting the front of the carburetor.
Rick
That's what I thought. There should be no vacuum source there. Going to have to look at the idle speed up unit to determine whether it's diaphram is leaking. It is mounted in the same area. Clay/Lexi
Yeah, it's tough trying to locate a vacuum leak with carb spray, with the fan blowing air all around.
Are you using a straw on the spray nozzle to help pinpoint the spray?
I hate having to even do that on a clean, painted engine because it can remove your paint.
Does that idle speed up unit use a hose to supply the vacuum, or is there a gasket over a passage? If it's a hose, remove it and cap the source and spray again and see what happens.
Rick
Cadman-iac, yes I use an extra long plastic nozzle-say a foot to a foot and a half long, to better direct the spray to target areas with more precision. Reduces blow back from the fan. The idle speed up unit receives vacuum from a port in the middle of the cast iron base at the firewall side. Metal tubing connects it to the idle speed up unit. There are also a pair of wires that fire the solenoid. Have removed this unit for now. Tough to get this carb to idle at a proper curb idle. Not sure what the problem is, but way off. Partly caused by the carpet jaming the pedal, with perhaps a wonky pivot point there. PIA. Clay/Lexi
Note: Filled threaded carb base hole with a blind plug for now.
Clay,
If you're unsure about if the carpet is interfering with the throttle linkage, you could temporarily disconnect your linkage from the carburetor and see if you can get the engine to idle correctly. If it does, then you know for sure the carpet needs attention.
If it doesn't make any difference, you know the carpet doesn't matter and it's definitely a carburetor issue.
Just a thought.
Rick
Don't forget that petrol these days is not as good as when these engines were built, and their carburetors calibrated.
I remember in the old days, one could get their engines to idle down to ridiculously slow speeds, and still run perfectly.
Bruce. >:D
Quote from: Cadman-iac on September 04, 2024, 01:28:46 AMClay,
If you're unsure about if the carpet is interfering with the throttle linkage, you could temporarily disconnect your linkage from the carburetor and see if you can get the engine to idle correctly. If it does, then you know for sure the carpet needs attention.
If it doesn't make any difference, you know the carpet doesn't matter and it's definitely a carburetor issue.
Just a thought.
Rick
Good point. Sometimes I over think things. why didn't I think of this? Yes, the new gas is not as friendly to our cars. Rebuilder said he opens up venturi slightly to help compensate. I also have a damp looking carb bowl gasket. After running, if you wipe your finger along the gasket edge, traces of fuel will be seen on your finger tip. Hoping the gasket will swell given time and stop this, as this carburetor has sat for about 5 years or longer. Any suggestions? Clay/Lexi
Something you may want to double check is your float setting. If the gasket is getting soaked like that, it's possible that the float is either set slightly too high, or it's not able to ride as high as it should due to other problems. What comes to mind is a small leak, or a build-up on the exterior adding weight to it which will cause it to sit lower thus raising your fuel level in the bowl. Either one of these will cause you problems with how it runs.
What I would do in this case is to check the setting as it is first, then drop the setting a small amount and test it to see if it makes any difference.
One consequence of a too high of a fuel level is not being able to adjust the idle properly.
As I phrase it, "The float don't".
The reason I suspect this is from what you've said about it, you haven't taken it out on the road yet, just testing the idle in your driveway or garage, so you're not getting any fuel "slosh" that would account for the wet gasket.
Just another thought. Hope it helps.
Rick
Edit:
One thing I would like to add, check to see if the float may be binding at any point in it's travel. This too can cause issues.
Thank you Rick. I did not know that a high float level could affect idle. And yes, no "slosh", just idling in the driveway as no motion. More stuff to check with little time as our driving season whittles away, :( Clay/Lexi
A sure sign that the float is too high is if you can close off your idle mixture screws and the engine will continue to run.
The higher fuel level allows the engine to draw fuel easier from the idle circuit and it can also just spill over into the engine in what I would call a controlled flood.
You can weigh the float, but unless you know what it's supposed to weigh, that doesn't do much good. A build-up of minerals or chemicals on the outside of the float or any fuel that might have seeped into it makes it sit lower in the fuel, letting the level go too high.
Unfortunately there's no way to actually see what level the fuel is inside the bowl, all you have is the specs for the float setting, so unless you have a brand new float, testing various settings is the only way to check.
On some Holley carbs, they have a removable plug in the side of the float bowl to visually check the setting, and some have external adjustments for the float as well. Both innovations stemming from just this sort of situation.
Good luck with your carburetor, I hope you find the problem soon. Gotta get Lexi back out and feed her for her upcoming hibernation, lol!!
Rick
Quote from: Cadman-iac on September 04, 2024, 12:27:46 PMGood luck with your carburetor, I hope you find the problem soon. Gotta get Lexi back out and feed her for her upcoming hibernation, lol!!
Rick
Feed for hibernation. LMFAO! These Rochesters actually have threaded plugs on the sides of the fuel bowl. I believe they are there to measure float height. Will have to look into this. Clay/Lexi
You got me thinking about those bowl sight screws and I thought I might have one of the 4GC carbs that had them, so I dug through what I have tonight.
Apparently this was not very common, out of 11 carburetors I had one with the sight screws. It's got one for each float, front and rear on the driver's side.
Screenshot_20240904-213641_Gallery.jpg
It's nice to be able to check the fuel levels, but you still have to remove the dozen or so screws and a pair of linkages to make any changes.
The engineers were on the right track, they just needed to go a bit further with this idea. It would have made carb adjustments so much easier.
Holley took it and ran with it and made it their own.
A few of my other 4GC carburetors had the bosses on the side of the bowl but weren't drilled out for it. I suppose it would be easy enough to drill and tap the bowl, but you would still need to locate the correct pair of screws for it.
This is also something that would only work on the Rochester 2bbl and the 4GC because of the bowl design. You couldn't do that with a Quadrajet.
The 4GC is also the only carburetor that can hold 2 quarts of fuel in the bowls. Kidding!!
When you pulled into the filling station back then you would tell the attendant to fill up the carb and check the tank. Lol!! I slay me!!
But seriously folks, I've always admired the 4GC carbs, they were impressive.
They probably were the reason why the government limited the size of the fuel bowl on later carburetor designs. The Quadrajet holds less than a 4th of the fuel that a 4GC does.
Can you imagine the size of the fireball you would have if you had a backfire with a 4GC?
If your fuel pump failed while driving you could still drive 8 miles on the fuel in the carburetor.
You could get home and park the car, come out the next morning and get half way to work before the carburetor ran out of gas!!
On that note I'll stop now.
Rick
Here is a shot of my carburetor with the 2 fuel sight plugs clearly visible. So they are there for float examination only and not to facilitate any float adjustment? Clay/Lexi
Quote from: Lexi on September 05, 2024, 09:03:51 AMHere is a shot of my carburetor with the 2 fuel sight plugs clearly visible. So they are there for float examination only and not to facilitate any float adjustment? Clay/Lexi
Unfortunately adjusting the float through the sight plugs would be like doing arthroscopic surgery. The pivot point/ adjustment point is in the front center of the carburetor directly below the fuel inlet. The only way to access it is to remove the top of the carburetor.
The only thing that the sight plugs do for you is let you know exactly where the fuel level is, which is helpful. If you get it set and check it through the plug, you'll know right away if you have to do it again or put the plug back in and drive away.
Rick
Clay, before you set the float level remove the floats and put them in a bowl of water and see if they float. If they don't float they have a leak ie.full of fuel. Don't ask me how I know this, also don't ask me how I know that if you try to resolder a fuel float it makes a very good flame thrower.🤣
One problem with the floats on the 4GC is that they are a dual float per bowl. You can have one half of one that is slightly heavier than the other side and it compromises the setting.
When you're checking them in water, look closely at it and make sure that both sides ride at the same level. Let it sit in the water and let the water calm, just quickly looking at it won't tell you anything other than it floats.
Also check to see that the arms going to each half are equal, that one isn't higher or lower than the other, that will mess up your setting as well.
Rick
Quote from: PHIL WHYTE CLC 14192 on September 05, 2024, 03:41:09 PMdon't ask me how I know that if you try to resolder a fuel float it makes a very good flame thrower.🤣
Tried that one myself. It didn't explode, but it got a lot heavier with the extra solder making it pretty much useless.
Quote from: PHIL WHYTE CLC 14192 on September 05, 2024, 03:41:09 PMClay, before you set the float level remove the floats and put them in a bowl of water and see if they float. If they don't float they have a leak ie.full of fuel. Don't ask me how I know this, also don't ask me how I know that if you try to resolder a fuel float it makes a very good flame thrower.🤣
I have heard that repairing them is very "ify" at best. I have lots of parts here, so would probably dig out a replacement set. Is it feasbile to drain any fuel that may be in there then patch any leak with JB Weld? Not sure I like the idea of that product sitting permanently in a fuel filled enviroment in my carburetor. Clay/Lexi
Quote from: Cadman-iac on September 05, 2024, 10:44:58 AMUnfortunately adjusting the float through the sight plugs would be like doing arthroscopic surgery. The pivot point/ adjustment point is in the front center of the carburetor directly below the fuel inlet. The only way to access it is to remove the top of the carburetor.
The only thing that the sight plugs do for you is let you know exactly where the fuel level is, which is helpful. If you get it set and check it through the plug, you'll know right away if you have to do it again or put the plug back in and drive away.
Rick
Well, thoroughly ticked off now. A rebuilt carb that is not performing safely. So I dug out a spare that I have had in storage for 4 years and installed it this afternoon. Works very well and car seems to be back where it was before all this nonsense began in early July. Ruined my driving season though. I was thinking about your comments Rick about basically controlled flooding (too high fuel level in bowl), and gasoline weeping through the gasket. Makes sense that it should not do that prior to driving the car on the road. I tried rapping the nozzle, hoping to perhaps dislodge any foregin matter that might be there. No luck. Car so far is now running great with my replacement carb from today's install. One thing I noticed is that although these are both 1956 Cadillac 4GCs, the one I just removed ran like a scared rabbit and I could not slow it down to idle properly. The one I installed this afternoon ran way to slow and would stall after fast idle off. Long story short, I got it running now but I have a theory that all of these carbs probably have more or less, some level of vacuum leak that may not have been there when new. Whether or not such are repairable or whether a service tech would even want to tackle some of these issuess, is debatable. My dislike for the idle by-pass screw system has also been re-enforced. As usual I had to do everything twice to get the car running, but Lexi can now hit the road and chow down on some Reynolds wrap imports prior to hibernation, LOL. Thank you for your sound advice (and humour) Cad-maniac. Clay/Lexi
Quote from: Lexi on September 05, 2024, 09:03:51 AMHere is a shot of my carburetor with the 2 fuel sight plugs clearly visible. So they are there for float examination only and not to facilitate any float adjustment? Clay/Lexi
Correct. Been following this thread
Quote from: Lexi on September 05, 2024, 06:35:27 PMI have heard that repairing them is very "ify" at best. I have lots of parts here, so would probably dig out a replacement set. Is it feasbile to drain any fuel that may be in there then patch any leak with JB Weld? Not sure I like the idea of that product sitting permanently in a fuel filled enviroment in my carburetor. Clay/Lexi
The issue with using JB Weld is that you're adding weight to your float, and I'm not sure if it would stay in place being submerged in fuel constantly.
Getting any fuel out of a float is difficult too. You either have to open up a hole in it so it'll drain, or maybe heat it and hope that the fuel can escape as a vapor without blowing it up in the process.
Then you'd still have to locate the leak, which isn't the same as looking for something escaping, but rather something entering.
You could try covering the entire seam between the two halves of the float, but like I said above, you're adding weight.
Rick
Quote from: Lexi on September 05, 2024, 06:48:02 PMWell, thoroughly ticked off now. A rebuilt carb that is not performing safely. So I dug out a spare that I have had in storage for 4 years and installed it this afternoon. Works very well and car seems to be back where it was before all this nonsense began in early July. Ruined my driving season though. I was thinking about your comments Rick about basically controlled flooding (too high fuel level in bowl), and gasoline weeping through the gasket. Makes sense that it should not do that prior to driving the car on the road. I tried rapping the nozzle, hoping to perhaps dislodge any foregin matter that might be there. No luck. Car so far is now running great with my replacement carb from today's install. One thing I noticed is that although these are both 1956 Cadillac 4GCs, the one I just removed ran like a scared rabbit and I could not slow it down to idle properly. The one I installed this afternoon ran way to slow and would stall after fast idle off. Long story short, I got it running now but I have a theory that all of these carbs probably have more or less, some level of vacuum leak that may not have been there when new. Whether or not such are repairable or whether a service tech would even want to tackle some of these issuess, is debatable. My dislike for the idle by-pass screw system has also been re-enforced. As usual I had to do everything twice to get the car running, but Lexi can now hit the road and chow down on some Reynolds wrap imports prior to hibernation, LOL. Thank you for your sound advice (and humour) Cad-maniac. Clay/Lexi
I would suspect the float setting is too high. If you had something lodged in the needle/seat you would have uncontrolled flooding until whatever was dislodged, then you would expect to not have any more issues.
As for how each carburetor performed, the first one was dealing with a high fuel level, allowing it to easily draw fuel from the bowl, and may have contributed to your high idle issue.
The second carburetor I'm assuming has the float level set correctly, sounds like you have all vacuum leaks fixed, and it just needs to be adjusted. Without being there to witness it running I'm just speculating.
But get out and let Lexi stretch her legs, feed her a turdbox or two before she goes into hibernation. Enjoy the ride and have fun.
No charge for the humour!
Rick
The Gods are not smiling upon me. Went to take the car out for a short test drive and was rough idling & tough to start. Smelled gas. Shut down immediately. Under the hood notice lots of uncontrolled flooding. Back to the drawing board. Yet with this carb which I only installed 3 days ago, (which ran fine when parked), it now also needs servicing. Looks like Rick's comment about blown needle/seat valve has now infected this carburetor. :( Clay/Lexi
Quote from: Lexi on September 08, 2024, 02:23:29 PMThe Gods are not smiling upon me. Went to take the car out for a short test drive and was rough idling & tough to start. Smelled gas. Shut down immediately. Under the hood notice lots of uncontrolled flooding. Back to the drawing board. Yet with this carb which I only installed 3 days ago, (which ran fine when parked), it now also needs servicing. Looks like Rick's comment about blown needle/seat valve has now infected this carburetor. :( Clay/Lexi
I'm really sorry to hear that Clay, it sounds like you're taking a page out of my play-book, or you're just having a Hee Haw kind of week/month or whatever. You know, "If it weren't for bad luck I'd have no luck at all, etc, etc, etc...."
Question, are you looking into these carburetors and making adjustments yourself, or just relying on your rebuilders expertise to get it right?
If it's the latter, maybe you need to consider taking up a new hobby, carburetor 101.
My issues this last couple of months have been with the quality of the parts I'm getting. F'ing Chinese crap not holding up like it's supposed to, but it's the only thing out there anymore.
Just today I put the second upper plenum assembly on my wife's car in 2 days. The one I installed yesterday began to split around the bolts after being torqued to the required 89 INCH POUNDS! Piece of crap plastic made in China.
This is the 5th one I've done over the years, so I know about the torque specs, and the last one went 7 years before giving up.
So today I installed large flat washers under the heads of the bolts to spread the load and hopefully the bolts won't just pull through the plastic like the one yesterday did.
Plastic has its uses, but engine parts ain't one of them!!
How many of these 4GC carbs do you have Clay? You may want to try and take the best parts from all of them and assemble yourself 1 good carburetor.
I was thinking about those air bleed screws, they are accessible from outside the carburetor, but they control an air passage inside the carburetor.
It seems that the issue with these is that the threads on the screws themselves are not airtight.
There must be a way to correct this, either by use of an O-ring on the screw if it has an area that would allow for that, or to use something like a thread sealant that doesn't solidify and lock up the screw.
I'll have to look again at my collection of carburetors and see if any of them use the air bleed setup. If I've got one, I'll see what if anything can be done to seal the screw from the external air.
But that's just one of the issues that you seem to be having.
The flooding issue would require a close examination of your floats, and the needles and seats.
It's funny, I'm fighting a similar issue, but with my Suburban and the throttle body injection. It seems that the computer and the camshaft are not getting along very well. As a friend of mine told me about the early computers they only have to monitor the air/fuel ratio and adjust the timing.
It's got two jobs and it failed one of those!
One day I'd like to wake up and everything goes right. Maybe next year that'll happen.
Rick
Been relying on the rebuilder. This latest carb was also rebuilt by him 4 years ago. It ran the car fine when removed, then I sent it out for servicing as I had another rebuilt unit to install on a newly rebuilt engine. Wanted everything new or rebuilt, a fresh start. So when I got that carb back I packed it up, where it has sat in a box for 4 years. Installed it this past Monday and it ran the car great. Best it has run in some time. This morning I wanted to ensure that the fast idle was not going to run the engine like crazy and perhaps spin my cam shaft, so I pushed the car out of storage to put eyes on the fast idle cam and also to be able to watch for any fuel anomolies (which cannot be done where it is normally parked). Cranked it a bit (without touching the gas pedal), to get some oil up into the upper block. Then put on the electric fuel pump to fill the carb bowl for an easy start. Right off I noticed an issue when listening to the E pump which after filling the carb bowl, it's sound usually modifies. Not this time. WTF I thought. Just sounded like it was still filling the carb. So I knew then that it was flooding the carburetor and engine. And it was. Gas all over the engine bay. So between parking it 3 days ago and this morning, something died inside it. Ruined the pavement. Can't win but for losing. But at least I got back under cover just prior to the light rain that later fell. Yes, it has been a horrible year.
As I have to be able to move the car, I put the other carb back on it which although it weeps a bit a fuel around the upper bowl gasket, it is not (yet) flooding it. So I got the car started with that one and parked her.
As for carbs, I have 3 useable ones, (all now requiring some work), plus 2 cores, as well as parts to make 2 or 3 more, all Rochesters. I also have a rebuilt Carter which has been stored for sometime, but might run as is. It came off of a Cobble Beach show car. I as well thought of putting an O ring on that idle by-pass screw to see if that will modify the air leak. Fed up right now. Seems I got to do everything 3 times or more. Was thinking the same thing; put one together myself with my best spare parts. This is a huge PIA. Hope my bad Karma did not pass on to you Cadmaniac! Clay/Lexi
Clay,
The idle by-pass screw is 50's technology that has been reinvented in the late 80's on fuel injected engines. It's called an idle air control valve, or IAC, but unlike the 50's version, this one is constantly adjusting to the engine load by the computer.
Unfortunately you can't adapt the electronic version to your 50's carburetor.
I looked at my carbs, the one with the sight plugs has an idle air bleed screw on the back driver's side. Where is the screw located on your carburetor? I keep thinking yours is between the primary and secondary throttle shafts on the driver's side, but I'm not sure.
Edit: I looked back through this thread and verified the location of the screw on yours, it is in a different spot.
Another question, when you had the carb rebuilt, did he re-bush the shafts, or were they ok?
I took the screw out of my carb and it measured 3 inches long. There's enough threads and they're fine enough that I don't believe that if any air were to get past the threads it couldn't be enough to really cause an issue.
As was stated earlier by someone else, the spring does two things, it keeps the screw from turning on its own and it puts pressure on the threads that would help in sealing.
I didn't get a chance to look closely at mine, so I'm not sure if there is anything that can be done to ensure a better seal. Your idea of using an O-ring under a washer and the spring pushing on both may be the best/only thing you can do.
On mine, there is no recess around the screw where it enters the base plate, which would have been an ideal place for an O-ring.
20240908_190915.jpg
Screenshot_20240908-202023_Gallery.jpg
Screenshot_20240908-202039_Gallery.jpg
Another thing I noticed about mine is it has slightly larger rear bores than the front. Like an early spread-bore design. Is yours like that?
Rick
Edit:
Just an update on my Suburban that has a bearing on this issue in a way.
Yesterday it was running really well and all of a sudden it was missing and stumbling on acceleration and the vacuum was really low according to my gage.
After checking the plugs again and the timing, I was just getting ready to adjust the distributor when I noticed that one of the vacuum lines had pulled apart. I put it back together and checked the rest of the vacuum lines and found the suction line to the vapor canister had also come off.
So after reconnecting both lines it ran just fine. Both lines are very small, but apparently they are still enough to mess up the computer.
You may want to trace all of your vacuum lines to check for leaks, disconnects, bad accessories or whatever.
I think someone else suggested unplugging all the things plugged into your carburetor and try running the engine again and see if it makes any difference. If so, then one thing at a time, begin to reconnect them and see what happens. When it starts to run badly again you have found the source of your problem.
If it still runs like crap after disconnecting everything, then you'll know the issue is internal.
I got lucky that I found those lines disconnected. I looked yesterday but I kept looking for something more serious, like a bad plug or wire, map sensor, IAC malfunction, ESC issues etc....not something as simple as a loose hose.
What's that saying or principle, keep it simple stupid, K.I.S.S.!!
Hey Clay,
I was just looking at my carburetor again thinking about how best to stop a possible air leak around that bleed screw. Just placing an O-ring on the threads with a washer to push it against the carb base will eventually crush the O-ring.
However, if you were to use a drill bit to put a small taper in the entrance for the screw for the O-ring to sit in, just a shallow depression, nothing to deep, then put the washer over it so it keeps the O-ring from coming out if you back the screw out, this would at least eliminate one possible vacuum leak for you. You could use a thicker O-ring so it would last longer as well. You will have to experiment with how deep a taper to make in the base, start small and increase if necessary.
I checked, the threads on mine at least, are a 3/8-18, a standard size, so if necessary to clean up the threads in the base after putting a taper in it, you can easily run a tap through it.
Just food for thought.
Rick
Here's a picture of a regular fine thread nut on the screw I used just to verify the thread size.
20240909_085651.jpg
Here's what I've come up with for the bleeder screw.
Screenshot_20240909-173749_Gallery.jpg
I would recommend using a fatter O-ring like one from a fuel injector as it's going to be stronger and resist being crushed by the spring and washer, plus it's made to handle the fuel, unlike most regular O-rings.
Here's a regular O-ring beside an injector O-ring.
20240909_173547.jpg
So you can see the sizes.
Screenshot_20240909-175447_Gallery.jpg
As you can see it's much more substantial and less likely to break and leak. And if you put a taper in the hole for the screw it'll help it seal even better. This was the base before I added a taper to the hole.
Screenshot_20240909-173916_Gallery.jpg
And this is after I tapered the hole.
Screenshot_20240909-174013_Gallery.jpg
With the taper there and the spring pushing it it'll form to the taper and that will also keep it from breaking and falling off. Just sandwiched between two pieces of metal, (the base and washer),it won't last long.
And here's what it looks like installed.
Screenshot_20240909-175129_Gallery.jpg
After being exposed to the heat of the engine the O-ring will eventually be pushed into the taper and form an even better seal.
I looked again at all of the 4GC carbs I have and this one is the only one that has the bleeder screw in it, all of the others are normal.
Hope this helps some Clay. Let us know how it goes.
Rick
Rick my thoughts as well, except I would not have thought about that fuel injector O ring. Good tip. Thanks! Earlier in this thread, (post #21), I uploaded 2 images of my idle by-pass screws. One looks near pristine, while the other has some obvious wear which suggests that it may be very slightly out of round. Looks similar to the one you posted an image of, with the same sort of wear marks. That could also add to the vacuum leak problems especially if the screw threads are not sealing. Do you think when these screws were new, even then they would have sucked in some brake clean during a test? Or would there have been virtually no perceptible leak rate? Clay/Lexi
Clay,
I doubt that any of those screws would become out of round unless they were put in a vise and beat with a hammer. They're just too thick, and the tip isn't tapered like a mixture screw would be, They're blunt ended, as they only meter air flow, and much more air flows through this than the amount of fuel that flows past the mixture screws.
As for the threads leaking air, it's possible, but I also believe that's why Rochester designed them with such a long threaded portion, to cut down the chances of too much air getting through from the threaded end.
Even a good throttle shaft and base will still have a minute amount of air seepage past the shafts, but in most cases it's negligible.
If you just put an O-ring on the screw with a washer over it as a test, (before you go to the hassle of tapering the screw entrance), then you can check for leaks around the throttle shafts without the bleeder being a possible positive indication because of its location on your carburetor, centered right between the two shafts. It would be really hard to tell exactly which one is leaking with them that close together as you spray, if that makes sense, at least on the driver's side, it won't make a difference on the passenger side.
Rick
Something I'm not sure about on your carburetor is how the air bleed air is distributed evenly with the outlet port being on the left side of the carburetor. Does your gasket have a passage cut out that directs this air into the center of the manifold/carburetor?
On mine, even though it's located in the back of the carb, the outlet port is dead center of the carburetor just behind the secondary throttle shaft.
Screenshot_20240910-101145_Gallery.jpg
Even on mine, being in the middle of the secondary throttle shaft, it's still not in the middle of the carburetor, (meaning dead center of the carburetor), so the distribution of air I would think would be more toward the rear half of the engine, which would cause a lean condition there, and a rich(er) condition in the front.
I've studied carburetors and throttle bodies and most will have a passage that dumps evenly to both sides on 2bbls, and towards the front or primary side on a 4bbl for anything that affects the air/fuel ratio, such as where the PCV connects to it. Too much air in one side leans that side out.
Unfortunately I don't have the base gasket that goes with this particular carburetor, so I honestly don't know if there's a channel to distribute this air evenly across the manifold so as not to cause any part to have a lean condition.
What does your base gasket look like for that carburetor?
I'm wondering if maybe you might have the wrong gasket that's causing you problems.
Just more food for thought.
Rick
Here's more on this. I took the base off of my carburetor to see where it gets the bleed air from and to see if maybe I missed an internal passage.
No hidden internal passage below the screw, it comes out right between the left and right secondary throttle plates.
But it does pull the air equally from both just above the plates in a channel cut between them.
Screenshot_20240910-104345_Gallery.jpg
So it is drawing filtered air here, HOWEVER, just above this point, in the gasket between the base and the body, it has those cutouts that are supposed to vent any fumes presumably to prevent hard starting, or a rich condition, and this just goes directly to the engine bay and comes out below the bowl in the rear.
(As you can see the gasket is in sad shape after sitting for who knows how long).
Screenshot_20240910-104329_Gallery.jpg
There are similar cutouts in the primary side of the gasket too.
Screenshot_20240910-130045_Gallery.jpg
Here you can see the evidence of the cutouts from the darker color of the base.
These are hidden between the bowl and base, nothing but dust could get through here.
Screenshot_20240910-130816_Gallery.jpg
There is a recess in the bottom of the bowl that may help keep dirt from getting sucked into the gaps in the rear as the engine is running.
Screenshot_20240910-125543_Gallery.jpg
Rick
It's been a long, long while since I messed with a 4GC carburetor, like 40 years now. I've forgotten a lot about them.
I was looking at a bowl assembly I had lying loose and I noticed that it has what I'd call an "equalizer passage" on the right side. It goes from bowl to bowl to keep the fuel levels the same between them, I'm guessing for times when there's a lot of bouncing or tilting up or down of the vehicle, and maybe even if one of the needles gets stuck.
Screenshot_20240910-132819_Gallery.jpg
It's not large enough to compensate for a stuck closed needle, but it might help keep a little fuel flowing from one to the other. The holes the fuel passes through are small and there's a restriction in the passage from one of the screws that hold the cover in place. They did drill through this and capped/plugged the access point as you can see in this picture.
Screenshot_20240910-132830_Gallery.jpg
There is a pressurized fuel passage that runs around the top of the cover that supplies both front and rear bowls.
Screenshot_20240910-135033_Gallery.jpg
Here's the float, both front and rear use the same type, so you can swap them without any problems.
Screenshot_20240910-132837_Gallery.jpg
I'm thinking about filling up one of the bowls on this just to see how much it holds.
Look at how big they are. Don't want a backfire if this leaks!
Screenshot_20240910-134145_Gallery.jpg
Clay,
What this has me thinking about what would happen if one of the floats was set higher than the other, and your carburetor has this equalizer passage in it?
You need to check both floats for the correct setting because of this equalizer passage.
I just looked at several of these carbs and they all have the passage.
Yes, a very over complicated carburetor for sure.
Rick
Quote from: Cadman-iac on September 10, 2024, 04:04:41 PMHere's more on this. I took the base off of my carburetor to see where it gets the bleed air from and to see if maybe I missed an internal passage.
No hidden internal passage below the screw, it comes out right between the left and right secondary throttle plates.
But it does pull the air equally from both just above the plates in a channel cut between them.
Screenshot_20240910-104345_Gallery.jpg
So it is drawing filtered air here, HOWEVER, just above this point, in the gasket between the base and the body, it has those cutouts that are supposed to vent any fumes presumably to prevent hard starting, or a rich condition, and this just goes directly to the engine bay and comes out below the bowl in the rear.
(As you can see the gasket is in sad shape after sitting for who knows how long).
Screenshot_20240910-104329_Gallery.jpg
There are similar cutouts in the primary side of the gasket too.
Screenshot_20240910-130045_Gallery.jpg
Here you can see the evidence of the cutouts from the darker color of the base.
These are hidden between the bowl and base, nothing but dust could get through here.
Screenshot_20240910-130816_Gallery.jpg
There is a recess in the bottom of the bowl that may help keep dirt from getting sucked into the gaps in the rear as the engine is running.
Screenshot_20240910-125543_Gallery.jpg
Rick
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Very interesting observations Rick, on a topic that as far as I know, has not been explored to this depth here. Guess we are breaking new ground. I won't fiddle with one of the carbs as the rebuilder who worked on it recently should make it right. In my spare time I am contemplating cleaning and rebuilding one of my spares on my own. In answer to one of your (?) earlier questions, putting a caliper into the disassembled carb, revealed that the bores for both primary and secondaries were the same measurement. The idle by-pass screw design seems intended to fit snuggly in it's passage much the same as the throttle shafts fit into theirs. One carb is back on the car, limping around. Other is packaged for return to the builder. One in pieces. Clay/Lexi
Hopefully your rebuilder will find the problem with it and get it back to you quickly so you can drive Lexi for a little bit anyway.
I did a test on this float to see if it was still good, it is. I wasn't sure because on one side it's got an extra spot of solder on it, and I was thinking it might not float as high in the water as the other side would, but it surprised me and floats evenly.
20240910_145025.jpg
I then did another test on the bowl assembly to get an idea of just how much fuel it will actually hold, as I've always been curious about that.
Using the float, (as it takes up valuable real-estate), I carefully measured water in a syringe and filled the front bowl. Not having the float connected to the top I had to estimate the correct level, (but it did sit level within the bowl), and I used the equalizer passage holes as a guide. And the rear bowl took just as much.
So with all this taken into consideration, it took as little as 4.5 ounces and can take as much as 5.25 to 5.5 ounces to fill it to the equalizer holes. It will depend on the actual float setting, but even given that, that's between 9 to 11 ounces inside this carburetor.
That's almost a whole can of soda!
It's no wonder why you walk away if it ever catches fire!!
I would consider rebuilding your spare yourself, there's enough information on here and people who can help if you have a problem, you have but to ask.
This is very similar to the 2bbl carbs of this time. It's like they took 2 of them and glued them together. Certain things on the rear half were changed so it wasn't duplicated, like the accelerator pump, and the idle circuit were left out of the rear half.
If you look at the venturi clusters they look like they could almost be swapped, but there are minor, critical differences between them. Mainly the idle air bleed passages and the accelerator pump passage and nozzles in the front cluster.
That will also give you some confidence in your ability to fix it should something happen on the road.
You need to know how to work on it if you're going to drive it.
Years ago I decided that I wouldn't have anything on my vehicle that I couldn't fix, and I was really hot for a long time, lol!! Then I learned to fix A/C systems. Same with the transmission, I was a shifting fool, then learned to rebuild automatics.
I hate having to pay someone to fix something I broke, so I learned to fix it myself.
One thing I'm not going to touch is a computer.
Rick
Very good advice. I should check my spare floats in case my current carburetor problem is traced to a faulty float. I am a lot like you as I do not like paying anyone to fix anything. Period. With cars I have exceptions, and carburetors is one of them as I just never got involved with them. Think I will delve into one of mine later this fall or winter. Do I need any special tools to work on them that I may not have? Clay/Lexi
I learnt years ago that if something broke, I had to fix it myself, or I couldn't use it.
That goes with cars, as I didn't like to walk once I got my Drivers' License.
Eventually, there was not much that I couldn't fix. I think of all that money I saved over the years. Especially on Apprentice wages.
Bruce. >:D
PS. Could never afford a new car. Still cannot, or wont. These days new cars are so bland.
Quote from: Lexi on September 10, 2024, 09:06:55 PMVery good advice. I should check my spare floats in case my current carburetor problem is traced to a faulty float. I am a lot like you as I do not like paying anyone to fix anything. Period. With cars I have exceptions, and carburetors is one of them as I just never got involved with them. Think I will delve into one of mine later this fall or winter. Do I need any special tools to work on them that I may not have? Clay/Lexi
For this carburetor there are no special tools required to disassemble and rebuild it. You could buy a float scale to weigh them with, but I don't remember ever seeing the specs for this one, so I wouldn't worry about that. Just checking that they float evenly is the main thing.
If you are going to take the throttle shafts out that's a bit tricky, but still not impossible. The risk here is just in getting the screws out that hold the plates in. They are staked on the ends to prevent them from backing out. A file will take the flattened end off the screws so you can remove them.
It's just paying attention to how things comes apart and following the rebuild kit instructions.
I would suggest that you take a lot of pictures from all angles before you start and continue as you go so you'll have them as a reference if needed since this will be the first one you've done.
I've seen some of what you have done, so I believe you can do this. Have faith!!
Rick
Quote from: The Tassie Devil(le) on September 10, 2024, 10:11:33 PMI learnt years ago that if something broke, I had to fix it myself, or I couldn't use it.
That goes with cars, as I didn't like to walk once I got my Drivers' License.
Eventually, there was not much that I couldn't fix. I think of all that money I saved over the years. Especially on Apprentice wages.
Bruce. >:D
PS. Could never afford a new car. Still cannot, or wont. These days new cars are so bland.
I agree completely Bruce, I don't like to have to walk either, although I could probably do with the exercise, lol!!
I learned how to rebuild standard transmissions after I twisted the input shaft in half in my 56 Chevy in 1982.
My first carburetor rebuild was necessary after I bought a rebuilt one and it didn't work. That was back in 1980.
Because I couldn't afford to buy a new car or pay someone else to fix what I broke, I had to learn quickly or walk quickly.
Most of us are probably the same way.
You're right about the new cars too, butt ugly!! Wouldn't have one if it was given to me, especially if it wasn't made here. The money made from the sale would certainly help to keep an old car running though.
Rick
Don't be afraid of the carb. They weren't that complicated back then. Just take a ton of pictures as stated above and you'll be fine. We did the one on our 55 7 years ago, and I hadn't done a carb since high school. I worked with my son on it and we had a good time. Didn't do the bushings tho.
Good words of encouragement. I will take the plunge. Gonna be off line for a chunk today, but using time to clean up shop and look for my small parts cleaner. Clay/Lexi
Seat valve stuck due to contamination. Cleaned out and OK now-car back on the road. Then at the coffee shop I noted a bulge or bubble, on one of my tire's sidewalls. Got to get that off for safety. Must have just happened. May buy a new set of tires, just don't know if I want Coker again. Yes, this "bubble" tire is a Coker with low miles. This has not been a good set. What has happened to Coker quality? Clay/Lexi
Clay,
Glad to hear you found the source of your problem and Lexi is now on the hunt for turdboxes.
Sorry to hear about your tire issue, but glad you spotted it before it caused you a bigger problem.
I'm glad one of us is having success at making something run. Still fighting my cam/computer war.
Congratulations on your first carburetor surgery.
Rick
Quote from: Lexi on September 15, 2024, 12:21:37 AMWhat has happened to Coker quality? Clay/Lexi
Since a long time, I have heard bad comments about this brand. I would never buy it!
Quote from: Roger Zimmermann on September 15, 2024, 02:37:39 AMSince a long time, I have heard bad comments about this brand. I would never buy it!
Coker has new owners as of a few years back and quality has taken a nose dive unfortunately
Quote from: Jon S on September 16, 2024, 08:10:23 AMCoker has new owners as of a few years back and quality has taken a nose dive unfortunately
Yes, the errosion of Coker tire quality seems to have begun around the time Harold Coker passed in 2014. Quality continued to slide after new company ownership which I think was in 2018. Very disappointed in my last set. Clay/Lexi
Quote from: Lexi on September 16, 2024, 02:40:51 PMYes, the errosion of Coker tire quality seems to have begun around the time Harold Coker passed in 2014. Quality continued to slide after new company ownership which I think was in 2018. Very disappointed in my last set. Clay/Lexi
It's a shame because they have a nice line of products. Even worse is the lack of quality from Kelsey Tire.