I"m sure this has been discussed many times already BUT can someone shed some light as to why I have an off idle stumble on my Holly 4000.

The 1956  -  312 engine has an automatic trans. Already have a 57 tach drive distributor in the engine and have done Teds 4000 mod to upgrade the teapots circuit to use vaccum advance.

Float levels seem to want to be high in this carb . When set at float level specs it hesitates horribly. No vaccum leaks. Timing is at 6 initial.  I did bump it a bit as far as 10 with no help in the stumble.

Both the vaccum and centrifical advances are working.

It goes from a dead stop with no stumble. Its only when I am at 30 MPH or so and give it some gas pedal that it stumbles.

Dont know what else to check or recheck.

Suggestions.

Oldmics

I recently had a bone stock 1956 Thundebird engine on the dyno and it had a stumble right off of idle.  Did the normal trouble shooting such as checking ignition timing, accelerator pump shot, the accelerator pump arm adjustment, air bleeds, fuel/float level, etc. and found nothing amiss.  I ended up rejetting the carburetor from #50 jets to #53 jets and that completely cured the stumble.  I attribute part if not all of this stumble to the ethanol laden fuels which makes the fuel mixture simply leaner.  This was confirmed with the wide band oxygen sensors that were mounted in the exhaust system while the engine was on the dyno.

Lorena, Texas (South of Waco)

That would pretty much dictate every 4000 teapot should certainty have its accel pump shaft set for the hole that produces the longest stroke, regardless of season/climate (unless most people in Florida or Death Valley have free access to pure gasoline)?

6 VOLTS/POS. GRD. NW INDIANA