Vacuum advance Diagnosis

ratlee2

What is the proper way to check vacuum advance. My '53 superwasp has a hestitation when accelerating and I want to rule out the vacuum advance. I discontected the vacuum line and put a vacuum pump with gauge on it. If I pump it up to 20 in of vaccum the advance moves, but the pressure slowly bleeds down to zero. Is this normal?



Rich

Unknown

Testing in your car, utilize a dwell and vacuum gauge.



1. Make sure the point and valve timing are correct. I.e. Point Gap and Distributor mechanical timing.



2. Start and warm the car to normal operating temp.



3. Connect the dwell meter and observe the dwell.



Use the specifications found at ALEX BURR or KEN CATES Websites



www.freewebs.com/hudsontech/



members.aol.com/stepdown53/STEPDOWNPG.html



Slowly advance the engine speed while observing the dwell meter... the dwell should smoothly increase as engine RPMs smoothly increase.



4. If the hesitation is still present... stop engine and disconnect the advance vacuum line to the advance canister. Cap the vacuum line. Attach a hand operated vacuum pump to the vacuum canister and restart the engine.



5. While observing the dwell meter increase the vacuum with the hand pump ... use the vacuum gauge to set the amount of vacuum to that found in the tune up spec. Changes in the vacuum should cause the dwell to change. If not the vacuum canister is not working properly.



Other issues. The distributor has a mechanical advance comprised of weights and springs. If there is dirt or other debris in the advance mechanism it will not operate smoothly. Broken springs are possible as well as corrosion. You have to take the distributor out of the car and remove the point plate to access these pieces.



Hesitation can be caused by other things, some suggestions:



Bad Gas

Failing or Failed Carb Accelerator pump

Plug fouling and gap

Valves and timing

Fuel delivery

Dirt in the carb

Vacuum leaks at the intake or to the distributor, at the Wipers



Hope this will assist you

Unknown

ratlee2 wrote:

What is the proper way to check vacuum advance. My '53 superwasp has a hestitation when accelerating and I want to rule out the vacuum advance. I discontected the vacuum line and put a vacuum pump with gauge on it. If I pump it up to 20 in of vaccum the advance moves, but the pressure slowly bleeds down to zero. Is this normal?



Rich

To answer your question, and assuming that you're using a hand held vacuum pump, the vacuum advance should respond quickly and not bleed down. It sounds like the rubber diaphragm in your advance is failing.



If replacing your advance unit doesn't help to eliminate hesitation, follow the other good advice offered above.

[Deleted User]

A 1 minute simple test would be to connect your timing lite. Check position at idle. Rev motor up 700 rpm or so and check the timing mark. If in same position or falls back to idle position location after a few seconds replace advance.

[Deleted User]

If you mean a hesitation when you hit the throttle, that will mean the accelerator pump in your carb is not working. Vacuum advance does not cause this.

[Deleted User]

It may be his accel pump. Just corrected a hesitation in a flat head ford this weekend due to a bad advance unit.

ratlee2

Thanks for the responses. I replaced the failed vacuum advance and capped the line going from my dual action fuel pump to my wiper (leaks as well). The idle improved, but still have the hestitation. I hestitation is present at from start to about 40 miles a hour. So I will look at the accelerator pump and mechanical advance next.



Rich