Holley 850 help
 

Carb has been rebuilt and still cant get to stop popping and missing and stumbling off idle. Once it gets going up around 2000 rpms it smooths out. Any ideas?

It has 6.5 power valve in front, plug in the back and the jets are 96's.

What are some of the engine details. Those are some big jets.

I agree. Are you sure you dont have a vacuum leak somewhere ?

They are gen VI chevy 454's crate motors, with dry exhaust, crossovers, and electric chokes.

Supposedly 425hp.

Fixx
 

Are you running thermostats with the cross overs?? Holleys hate it when they are cold..long process and its hard to diagnose over the key board..post a video on youtube and let us hear what its doing and we can some how figur it out..first i would make sure the timing is spot on,,the air fuel mixture screws and idle set screw go hand in hand with each other,,if the idle set screw is set to high the engine will run out of its idle circuit and will stumble at all times..pm me your phonne number and i will call you to go over some things..

No thermostat and timing is correct.

Is the back of the transom blackishly sooty ? Who jetted the carbs ? Who dialed in the carbs after they were installed on the motor ? Float levels good ? Air mixture screws adjusted right ? Proper base gaskets used ? Carbs tightened down correctly ? Air bleeds clear ?

I personally think thats a little too much carb for your motors....and I also think your way heavy on the jetting. :drink:

Too much jets. I run 89 front and 86 rears on my 468 now and I still think it's too rich!
Also, your static timing plays a big role with idle smoothness too.
My thoughts are your jets are off though. I'd start there and see how you go.
Good luck!