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Have an out of the box 750 Double Pumper.

I cannot get it to lean out for the life of me

440 4 spd with 10-11 of vacuum at idle (very irradtic very hard to pin point exactly)

I went down to a 4.5 power valve from a 6.5 and a 73 jet in the primary to a 68 (I do understand that they aren't factors at idle, just mentioning the changes)

The 4 corner idle, I can bring 3 of the 4 all the way close and it still runs.

It will still run with the front 2 closed

I started at the 1.5 turns on all of them and little to no change in vacuum

could it be a defective carb?

I checked everywhere for vacuum leaks, there are none I can detect

thoughts?

Just an idea but is fuel psi good for that carb.?

Set at 5-6 Psi Holley Blue Top with regulator

Are you sure the throttle plates are closed?

Is this a bad time to tell you how to fix a Holley for good?


...replace it with a Carter! LOL

What car is this in?

The 4 speed Rich

I've had very good luck with the Holleys in the past, this one is stumping me a bit.

Tried tweaking the plate and its still not having an affect

The cam may have something to do with it of course, I think its a big overlap as well the car likes a lot of initial timing

The 850 I had on there ran extremely well (albeit always burning rich) but I wanted something a little tamer so I don't smell like and exhaust pipe when I get out of the car!

Are the float levels set ok? Sounds like you have covered everything else well?

Yes Sir, just trickling out of the site plug when you give it a bump

Everything I am reading seems to point to opening up the secondary throttle plate, I think I need to revisit that setting (open it more) and give it a whirl

Throttle plates could too far open. Sounds like it could be drawing fuel from the transfer slots at idle making the mixture screws ineffective. Are there holes in the throttle plates? I've had luck with drilling 1/8 holes in the throttle plates to allow more air go thru the plates instead of around them.

I went thru this same senario with my car - the ultimate fix was a locked distributor. It sounds like your problem could be the low vacuum - if the carb is old and worn it will need even MORE vacuum to work correctly. Unfortunately - you will need a start retard if you run a locked distributor and probably have to shut off the engine in gear to prevent run-on.