Holley Experts: Stumbling?

[doc540]

Everything has been copacetic for over a year, but recently my Holley 390 on the Slant has started stumbling right "AFTER" acceleration.

It's not hesitating from idle to go, just slightly stumbling JUST PAST depression of the pedal.

Jets, nozzles, accelerator pump, vacuum advance have all been changed earlier with the timing adjusted properly when out of the blue it starts this stumbling. No vacuum leaks. Unhooked the vac advance and plugged the carb tube - had no effect. Timing mark's right on the money (and hasn't been changed).

Hot/cold, doesn't matter.

It even stumbles at slow cruising speeds (below about 50mph) right after mashing the gas.

Worked perfectly and started this without anything else being changed.

What say you?

 

[hoosierdaddy]

accelerator pump ?

 

[teringer]

check wiring on the pick up in dist for a rubbed thru spot and a bad plug wire.double check the gap at pick up coil

 

[Mattax]

Old fuel leaves a varnish - if it sat
Slowly accelerating is OK? If so, then go over the accelerator pump system. If it uses a rubber umbrella check valve, it may have become distorted by the latest fuel mix. IIf not, then a passage could be clogged, reclean circuits.
Always Check fuel level in the bowls.

 

[doc540]

removed the front bowl, cleaned everything with carb cleaner, nothing looked gunked up (full kit not too long ago)

Seems to accelerate more consistently, but I'll have to drive it midday to get it up to full operating temp to test it.

Thanks for all the suggestions.

 

[AJ/FormS]

Blow out the airbleeds, then
Back to basics
valve lash and compression test

 

[jimjimjimmy]

it sure sounds like it is in the dist maybe the advance springs .

 

[doc540]

drove it at full temp today - much improved

thanks