1960 Runs good with or without

[60eldo]

 So was driving my car today and it runs just as good when I remove vac line from dist. It has electronic ign,,,is that why? I tested the carb and wen I rev it,,,,it does pull vacumn

[The Tassie Devil(le)]

Something sounds fishy to me when you can have an additional Vacuum leak, by pulling off the Vacuum Advance hose and it runs okay.

But, when you reconnect the Vacuum Advance, does the timing change? (Visible by using a timing light)

Bruce.

[60eldo]

 I will check in the morning,,,but tell me if im rong,,, theres no vac at idle, how can it change

[The Tassie Devil(le)]

There should be the most vacuum at idle.

Then at full throttle, the throttle plates are open at their widest, and therefore all the air entering the intake manifold is coming down the carburettor holes, and therefore not much use for the Vacuum Ports.   Therefore the Vacuum signal dies down.

When the throttle plates are closed, the intake manifold  (engine) is trying to get its' air in any way it can.   The throttle plates are closed, so the next place is the open ports, hence the air is being pulled in, creating a vacuum at the end of the ports (hoses).

That is why Vacuum is strongest at idle.   The intake stroke of the descending pistons is trying to pull in air, but the throttle plates are limiting this flow.

Bruce.

[James Landi]

"Under a light load and part throttle conditions, timing is advanced by way of the vacuum advance. This improves throttle response and makes the engine more efficient. It also helps the engine run cooler. The vacuum advance provides this benefit BEFORE the Mechanical Advance provides Total Timing."


Many of us run our cars with broken vacuum advance because a non functioning advance is difficult to discern --yet it's- easy to check, with the distributor cap off and a rubber hose connected to the advance, one can simply suck on the hose and literally see the stator plate move in response to the vacuum you apply... when tuning an engine with a timing light, a working vacuum advance is to be disengaged and the vacuum line is intentionally plugged.

[60eldo]

  When car is running at idle speed there is no vac at the carb port where the hose goes in from the dist. When I rev the engine there is lots of vac. Engine  vacuum, available above the throttle plates of a carburetor, used to advance ignition timing when the throttle is opened above its idle position.

[klinebau]

Does this carburetor have a ported vacuum port?  Ported vacuum means that there is no vacuum until the throttle plate is opened a little.  Some carburetors have two types of ports to expose vacuum at idle or not.  If you have a ported port, then this is what was used at the factory to connect the vacuum advance.  Determining which is better to use for the vacuum advance is a matter of debate.

[60eldo]

Yes my carb has ported vacuum. And thats where the hose is going to from the dist.

[TJ Hopland]

I'm not clear what the issue is.   It performs better with it disconnected?  Or it doesn't make a difference if its connected or not?    The electronic conversion doesn't usually change anything about how the timing works, its still mechanical with the fly weights and vacuum.

If you had an engine 'in time' with points and then install an electronic conversion chances are good the timing will change some just because of being different components.  Say it was at 10* before the conversion it may be at 15 after so you just need to re adjust it after the install to get back to where you started assuming that is where you wanted to be.

[60eldo]

   TJ, it runs the same weather its conected or not. If I drive with vac off the carb and I plug the carb, it runs great.

[Cadman-iac]

TJ, it runs the same weather its conected or not. If I drive with vac off the carb and I plug the carb, it runs great.

 Jon,
 It sounds to me like your vacuum advance unit is bad. If you apply vacuum and have no change in the way it runs, the diaphragm is bad.
 Have you checked it with a timing light to see if it changes the timing?
 It's easy enough to do at an idle, but you will need to use a manifold vacuum source instead of the ported source you have now.
 
 Rick

[60eldo]

I just tryed that, went to manifold vac and the timing changed with timing lite, so seems diafram is good. Now , why when I disconect the hose at the carb and plug the carb, it still runs good. Shouldnt it run like crap.

[Cadman-iac]

I just tryed that, went to manifold vac and the timing changed with timing lite, so seems diafram is good. Now , why when I disconect the hose at the carb and plug the carb, it still runs good. Shouldnt it run like crap.

Not necessarily if it's tuned right. By how much did your timing change though? If it was only 5 to 10 degrees, the diaphragm might still be bad. I've seen some that will work/move up to a point where it will uncover a hole in the rubber and it won't move any farther then.
What is your initial timing set at without the vacuum connected?
If this were my car, I would use the ported vacuum since it seems to run just fine without any advance at idle. Use the vacuum to add more timing at higher RPMs where you need it.

Rick

[Clewisiii]

When I had my distributor rebuilt they also rebuilt my original Vacuum Advance.




I wanted to have a spare, so I was hunting one down and was shocked at the price people were asking for one. I managed to find a NOS aftermarket replacement for $45. I will keep this around.

[bctexas]

Hi Jon,

According to my old Niehoff tune-up chart centrifugal advance should be 7-9 degrees at 2000rpm, and vacuum advance 11.25 degrees at 13-15 in vacuum.  (The ".25" bit seems a bit odd but there ya go.)  Did the changes in timing you observed with your timing light look to be around these values?  If so, you should be fine.  I'm not so sure you can tell from casual driving whether or not the vacuum advance is working.  But I suspect you would see a measurable decrease in fuel mileage if it wasn't working.

Happy Motoring!

[The Tassie Devil(le)]

I realise that what I am doing is against the factory method of doing things, but I like to convert the Vacuum Advance to full Manifold Vacuum.

This way i get the best performance I want out of an engine.   Ported Advance is for meeting the Federal anti-pollution figures.

Bruce.

[TJ Hopland]

I have had some engines that seemed to run best on ported vacuum.

[The Tassie Devil(le)]

Ford cars use the Ported Vacuum.

Anyone using a Holley Carby needs to know that the Vacuum Port on the side of the Metering Block is Ported Vacuum.   Putting a Holley on a "normal" engine (Not Ford) must use full Manifold Vacuum to gain the best performance.

Bruce.

[James Landi]

"I realise that what I am doing is against the factory method of doing things, but I like to convert the Vacuum Advance to full Manifold Vacuum."

Knowing that you and I have posted on the subject of vacuum advance technology, I feel bad for those CLC members who think that just because it's bolted onto the side of their distributor that it's working, and I entirely agree with you that directly connecting a working advance to the manifold yields better results with regard to accelerator responsiveness, better gas mileage, and cooler running engines.   James

[TJ Hopland]

How much does the vacuum move the timing?  And at what vacuum readings?


I don't know how many options there were that early but for sure by the time you got to the 70's there were dozens of different vacuum advance units from the factory that had different amounts of travel and different rates.  As time and aftermarket went on all those options got boiled down to just a couple options that sort of fit all but not. 

I have dealt with several cars where things just were not responding right and when I finally looked up the correct specs the replacement unit was doing 2 or 3 times the timing from what they should have been doing so you really need to have access to the original specs (if the engine is still mostly original) and the tools to be able to test it like a hand vacuum pump/gauge and ideally a dial back timing light.

Maybe in this case the vacuum advance doesn't have much/enough range for some reason?  11 degrees should be something you could hear or feel with a properly calibrated buttdyno. I don't know that I would say it would run like crap.  Lack of vacuum advance usually just kinda gives flat performance. 


Ford had what I think they called 'load-o-mattic' that I don't think used weights, it only had the vacuum portion which wasn't just ported it also involved what looked like a Holley power valve. Those were for sure a problem if you messed with either the carb or dizzy,  you needed the matched set which I believe was always an Autolite carb and Autolite dizzy.  I know they used that in the 60's not sure if it made it into the 70's or not.