Alcohol Holley 1050 HP Stumble Help Needed

[dragstang86]

I have an alcohol 2 circuit Holley HP 8082-3 1050 carb with 2011 metering blocks that I have been fighting a stumble between around 1800- 2600 rpm off a footbrake launch. Car is crisp below 1800 or above 2600+ rpm but looking for some reaction time adjustability in the middle. I recently put thr BLP anti stumble kit on it with the 70cc pumps, massive cams and larger squirter screws which seemed to help but didn't quite eliminate the stumble. I also have the squirters and accelerator pump passages in the bowls drilled out to the same size as the metering block/large squirter screw passage size for maximum squiter volume. Idle air bleed is .061 and have the idle screws 2 1/2 turns out. I've considered trying the Thompson Performance squirter plates but not sure if they are snake oil or not? Engine is a 415 sbc with 10 degree heads. Thanks for any advice you can offer.

[dragstang86]

Well I tried raising the idle pressure to 3 pounds (belt drive pump) and that seems to have helped it seems to only have a slight hesitation between 2000-2300 now according to the tach ( 1800-2100 according to Grid). Anything above or below that range is crisp.

[bigblockmark]

Why not try to increase the idle pressure a little more with smaller jet in the return or different pully size. 4#? How much pressure going down track now?

Does it have an adjustable transfer slot restrictor? Might find something there.

[dragstang86]

[bigblockmark]

Have run as much as 13# at WOT before on Alky.

[ojh]

At 2 1/2 turns out on the idle screws you are very close to having a vacuum leak, when the idle screw is fully out there will be a direct vacuum leak (you'd think fuel would come out) and it'll actually work like another really large idle air bleed. Run them in a full turn and see what happens.
Has the engine temp remained the same while you are trying different things with the carb? It'd be nice to know the front to back heat range on the head to see if you have a fuel distribution issue that you are fighting.

[dragstang86]

[dragstang86]

[GTO Geoff]

The post by OJH about a vac leak '& fuel coming ' out past the mixture screw is incorrect.

Engine vacuum is being applied to the idle cct, which 'sucks' fuel IN, not out.

Mixture screws being out 2.5 turns is probably a symptom of another problem. Idle fuel comes from the idle port [ mixture screw ] + T slot. Could be the t/blades are nearly closed at idle, closing off the T slot. With very little or no fuel available from the T slot for idle, the mixture screws need to be backed out MORE to provide enough A/F mixture for idle.
If the engine idles/runs ok, leave it.

[dragstang86]