[randy]

I have a hesitation problem I have been argueing with for years. It occurs when I'm lightly accelerating from idle or at low RPM's [less than 2000 ] and accelerating lightly.Accelerator pump works fine.I have an advance timeing light and it's showing my timeing is retarding 4-6 degrees on acceleration. Do I possibly have the wrong vaccum advance? Any thoughts?

[randy]

I have a hesitation problem I have been argueing with for years. It occurs when I'm lightly accelerating from idle or at low RPM's [less than 2000 ] and accelerating lightly.Accelerator pump works fine.I have an advance timeing light and it's showing my timeing is retarding 4-6 degrees on acceleration. Do I possibly have the wrong vaccum advance? Any thoughts?

[Rocky Rotella]

A sure fire to see if your vacuum advance is acting up is just disconnect it and plug the line to it. If you're checking timing with the vacuum advance system hooked up, it'll throw your numbers way off. First try the test drive without the vacuum advance. You may have to purchase an adjustable unit and limit the amount or travel and vacuum.

You say your accelerator pump works fine. Can you visually see the pump shot in the primaries? Also, you may have a bit too much tension in the spring or a binding action of the pump cup. Are you using the stock pump and return spring? The carb may have some crap in the passages too. I just worked on a Q-jet here that had fuel/moisture "gel" in the passages. I use carb cleaner, a wire and compressed air to clean it out. Works much better now.

[randy]

I've checked timeing with advavce disconected and vacuum line plugged.A test drive with no vacuum advance showed little change.A test drive with a check valve in the vacuum line to the distributor almost eliminates the problem. Pump discharge is a little light on one side. I'll get that cleaned up tomorow. I'll also check my supply of pump springs for a weaker one.Does adjustable advance simply limit travel or does it change vacuum also?