What triggers a carburetor rebuild?

[chrisbutnut]

How does one know when a carburetor needs to be rebuilt?  For a car with 99,000 miles that basically runs well, as far as my untrained eyes can tell, is there any benefit (or risk) to having it rebuilt?  I've read about Bowen Carburetor, however I live in Oregon, so that would require me to remove and ship the carburetor.  I'm not sure that I'd be comfortable removing it and then putting it back and trusting that the engine would run properly.

[Michael Petti]

Unless you are consuming fuel at a rate much below 10 mpg and/or performance is poor, I would leave it alone. Clean it with spray cleaner and run Seafoam through it per instructions and be happy it works well. If it ain't broke don't fix it.

[Clewisiii]

When I got my car it had not run in over 30 years. So I knew the carb would be bad. I pulled it and sent it off for rebuild.




With the rebuild they set it all up and tested it on an engine and shipped back to me.



This ended up sitting in a box for 3 years until i had my engine rebuilt.



I did nothing to the carb. It was only engine timing adjustments that were needed to get the engine running nice.  You may need some tunning as you work with it. I am sure that I still need more once I am able to run this engine on a road. But a good rebuilder should give it back in a ready to use condition.

[David Greenburg]

The  most obvious symptom would be leaks or flooding. Beyond that, assuming tune up components are good and properly adjusted and fuel filter is good, poor performance such as stumbling or lame acceleration. You don't say what year/type you have. Unless it's something  very old and unusual, like a V-16, there certainly should be shops around PDX that could evaluate and, if necessary rebuild it. OTOH, my understanding is that the good "mail order" places bench test them, so the car should run when you get it back and you can take it in for fine tuning if you don't want to do it yourself.     

[dn010]

Over the years, you'll get fine debris that will settle to the bottom of the bowls and some varnish from the fuel on the bowl walls. If you run today's ethanol fuel, you'll get some gummy fuel pretty much everywhere if the car isn't run and the fuel sits.

The debris and varnish are inevitable and you can run many years that way.

The gummy fuel will cause eventual problems and you'll know then that you'll need to rebuild.

Right now, I'd also suggest to leave it alone.

[TJ Hopland]

What year and model are we talking about here?  Some carbs have more 'soft' parts that are more prone to aging than others. 

Sitting is often harder on them than regular use.  The types and quality of fuels you use and or that are available in your area effect how often they need work as well as the ambient conditions.         

[Lexi]

Agree with the previous comments, best to leave it alone right now.

To me, a "bench test" means the carb is hooked up to a flow tester. I believe mineral spirits are run through it. Don't think this is a combustion process type test, like what you have when the carb is actually re-installed back on your car. I prefer to use a rebuilder who tests their rebuilt carb work on an actual engine. That is more accurate as one is bascially comparing apples to apples as it is installed on a running engine, usually in the shop on an engine stand for this purpose. Your carb/system may still need some tweaking when you get it back, for various reasons.

Could things go sideways? Yes, always the possibility of something going wrong, BUT... if your carb is acting up and in need of servicing, a rebuild out weighs the possibility of a servicing error. Possible rebuild issues could include, but are not limited to: a gasket leak, debris left in a chamber from the rebuild, "tanked" for too long with the chemistry eating away key parts such as the bakelite choke housing. Happened to me. The choke cover disappeared as was eaten away. Rebuilder forgot about how long my carb had sat in the cleaner. I think it could eventually pit the metal in a worst case scenario. Other issues may include a mismatched accelerator pump, perhaps increased if you do not have your actual carb tag number for referencing. That said, I believe a competant rebuilder should be able to tell by feel, if the replacement pump plunger fits properly. Clay/Lexi

[Cadillac Jack 82]

Biggest problem is getting the right person to rebuild it.  Even experienced shops may overlook something or do something wrong, depending on their workload.  The 59s carb survived the engine fire and only took cosmetic damage.  Still runs great after a thorough cleaning and checking seals.  A friends 61 Carter was rebuilt locally by a shop that usually does stellar work, and he's had nothing but issues since then.  Turns out the metering rods were incorrect and other parts cheap import parts from China.

[chrisbutnut]

I really appreciate the input!  My car is a 68 Coupe DeVille.  I wouldn't say that there are any current issues, per se, aside from an idle that is just barely on the rough side and then acceleration that seems a little sluggish for an engine of this HP and torque.  Then again, this is my first classic car, so I really don't know what to expect. 

[dn010]

other parts cheap import parts from China.

THIS is a huge problem. A year or two back, I refreshed an Edelbrock 650. More than half the parts in the rebuild kit could not be used. Some of the gaskets could not be used. The floats were useless. Anyone rebuilding these should try to use as many of the original parts that came out of it that can be reused.

I really appreciate the input!  My car is a 68 Coupe DeVille.  I wouldn't say that there are any current issues, per se, aside from an idle that is just barely on the rough side and then acceleration that seems a little sluggish for an engine of this HP and torque.  Then again, this is my first classic car, so I really don't know what to expect. 

This could simply just be maintenance items - plugs, points, wires, cap & rotor and the like. It's amazing what a fresh tune-up can do for your engine.

[tcom2027]

I was in my mid thirties when they were new. They RAN. If it's accelerating OK, with no hesitation and you are getting good mileage with it leave the carb alone. except setting the idle wit a vacuum gauge, or just do it by ear.

 It does sound like it would benefit from a tune up. Compression check, plugs and points if necessary. Condenser too because every one replaces it regardless of condition. Check the resistance of the spark plug leads. If it's OK and the leads aren't burned or cracked reuse them. clean the carbon from the inside posts of the distributor and check for cracks. The caps are virtually indestructible. If there are no cracks and the posts aren't grooved reuse it. Make sure the choke is set properly and the high idle pull down etc,is working fine.

THose engines aren't like the modern engines which are virtually silent mostly because of computer controlled fuel metering and overhead cams. On the old pushrod engines timing chains wear and stretch, small vacuum leaks develop AIR systems leak. Tiny amounts of leakage from all those sources contribute to a less than electric motor smoothness to an engine. If I were you I'd take the time to replace the rubber vacuum lines or at least clip the ends where they connect to the carb, distributor, brake booster. Cheap fix. Replace any that are soft or mushy. The 68s have an AIR (air injection reactor)system, a primitive pollution device that relies on an air pump. Vacuum leaks can develop in that system. Many owners disable it, especially here in California where '76 and older cars are exempt.   

If you are a car show trophy chaser and have to have the "correct original" carb, check with Daytona Auto Parts in Smyrna Beach Florida. I had good luck with their rebuilds.

Maybe dump some seafoam through it, might help can't hurt. I never did it. If that, along with Gumout or any spray bomb cleaner doesn't work just get an Edelbrock from Summit. THey are matched to the engine by compression ratio and displacement. Rather than screw with the Rochester on my '67 DeVille, I got an Edelbrock carb from Summit, bolted it on, adjusted the idle and the car ran like new.

I can overhaul those carbs, but the kits available aren't of the greatest quality. I'm really not willing to fight removing jets, rebushing throttle shaft bores, bending links and spending a six packs worth of time truing the base using emery and a surface plate. ANd still have the car runs 80% of new.
 
Read through some of the threads here by owners who have had problems with the Rochesters and Carters of that era and see what it took to correct their problems.

FInal note on smoothness: WHen I was at the NAtional held at Phoenix Arizona many many years ago I walked past a '41 75 series or it may have been a 63 series with the hood up and the engine idling. I could barely hear the engine, It was probably turning 450/475 RPM and was one of the quietest engines I'd been around. THe car had less than 30K miles on it and had belonged to the Diocese of San Francisco. I asked the owner if he would close the hood. He did and I couldn't hear it standing  within a few inches of the front fender. The exhaust was extremely quiet and smooth sounding.The owner may still be a member of the Club.

So what does that have to do with a '68 with a less than perfect idle. Probably nothing but it shows that classics can be very smooth running and idling if maintained properly. One of the reasons modern rebuilds of the 346/322 engines don't sound like when they were new isn't that the rebuild was careless. The lifter blocks wear and NOS blocks aren't available. Most important, while repro plungers are avaiable, they are not matched to the lifter bodies like the factory parts were. Same with getting the valve stem length within a few thousandths in spite of there being a pretty wide spec for their OAL.

Way more than enough for now. I feel writers cramp coming on.   

[chrisbutnut]

I was in my mid thirties when they were new. They RAN. If it's accelerating OK, with no hesitation and you are getting good mileage with it leave the carb alone. except setting the idle wit a vacuum gauge, or just do it by ear.

 It does sound like it would benefit from a tune up. Compression check, plugs and points if necessary. Condenser too because every one replaces it regardless of condition. Check the resistance of the spark plug leads. If it's OK and the leads aren't burned or cracked reuse them. clean the carbon from the inside posts of the distributor and check for cracks. The caps are virtually indestructible. If there are no cracks and the posts aren't grooved reuse it. Make sure the choke is set properly and the high idle pull down etc,is working fine.

THose engines aren't like the modern engines which are virtually silent mostly because of computer controlled fuel metering and overhead cams. On the old pushrod engines timing chains wear and stretch, small vacuum leaks develop AIR systems leak. Tiny amounts of leakage from all those sources contribute to a less than electric motor smoothness to an engine. If I were you I'd take the time to replace the rubber vacuum lines or at least clip the ends where they connect to the carb, distributor, brake booster. Cheap fix. Replace any that are soft or mushy. The 68s have an AIR (air injection reactor)system, a primitive pollution device that relies on an air pump. Vacuum leaks can develop in that system. Many owners disable it, especially here in California where '76 and older cars are exempt.   

If you are a car show trophy chaser and have to have the "correct original" carb, check with Daytona Auto Parts in Smyrna Beach Florida. I had good luck with their rebuilds.

Maybe dump some seafoam through it, might help can't hurt. I never did it. If that, along with Gumout or any spray bomb cleaner doesn't work just get an Edelbrock from Summit. THey are matched to the engine by compression ratio and displacement. Rather than screw with the Rochester on my '67 DeVille, I got an Edelbrock carb from Summit, bolted it on, adjusted the idle and the car ran like new.

I can overhaul those carbs, but the kits available aren't of the greatest quality. I'm really not willing to fight removing jets, rebushing throttle shaft bores, bending links and spending a six packs worth of time truing the base using emery and a surface plate. ANd still have the car runs 80% of new.
 
Read through some of the threads here by owners who have had problems with the Rochesters and Carters of that era and see what it took to correct their problems.

FInal note on smoothness: WHen I was at the NAtional held at Phoenix Arizona many many years ago I walked past a '41 75 series or it may have been a 63 series with the hood up and the engine idling. I could barely hear the engine, It was probably turning 450/475 RPM and was one of the quietest engines I'd been around. THe car had less than 30K miles on it and had belonged to the Diocese of San Francisco. I asked the owner if he would close the hood. He did and I couldn't hear it standing  within a few inches of the front fender. The exhaust was extremely quiet and smooth sounding.The owner may still be a member of the Club.

So what does that have to do with a '68 with a less than perfect idle. Probably nothing but it shows that classics can be very smooth running and idling if maintained properly. One of the reasons modern rebuilds of the 346/322 engines don't sound like when they were new isn't that the rebuild was careless. The lifter blocks wear and NOS blocks aren't available. Most important, while repro plungers are avaiable, they are not matched to the lifter bodies like the factory parts were. Same with getting the valve stem length within a few thousandths in spite of there being a pretty wide spec for their OAL.

Way more than enough for now. I feel writers cramp coming on.   

Thank you for the info!

[Lexi]

As usual, an informative and interesting post by Tony. Clay/Lexi

[tcom2027]

As usual, an informative and interesting post by Tony. Clay/Lexi

Thank you.

tony

[Lexi]

Actually I was hoping to read more.     Clay/Lexi

[tcom2027]

I thought that my post and other contributors  to the thread pretty much covered the subject.  Along with that I considered  you and the OP might suffer sensory overload  by the time you got to the end of my post. 
tony