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Old 12-30-2005, 07:38 AM
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Holley rich at idle

Guys,
Hapy New Year. I have a '35 Chevy with a SBC400 in it. I have upgraded to Allum heads (Dart Pro) and Edelbrock Air Performer and a Holley Avenger 750. Engine runs great and strong from about 1800 RPMs to 4500 RPM's. For an old guy, I go fast enough at the 4500 top end.

My problem is that my car runs entirely too rich at idle with massive amounts of unused gas coming out the exaust. If I manually floor the carb from idle, it will sometimews backfire but always seems to just momentarily die. If I moderately increase the throttle, it works great and is using every bit of gas it can get. I was told to increase the jets but won't that increase the richness at idle also. Any help would be appreciated.

Thanks
Paul

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Old 12-30-2005, 08:17 AM
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You may be running too low vacuum and the power valve circuit is opening or your throttle blades have uncovered the transistion circuit.

Part of the backfire is due to insufficient accelerator pump response to the opening of the throttle.

Have some one hold the gas pedal floored. On the accel arm is an adjustment. You need to have 15 to 20 thou of clearance between the lever on the bottom of the bowl and the spring assembly.

I have found the pink cam I think #330 in the number 2 hole on the shaft and #3 hole on the cam with a 31 discharge nozzle usually a good starting point.

Measure your vacuum and the power valve should be 1.5 to 2.5 smaller than the idle vacuum. To get the throttle blades to close and cover the transistion circuit, you can slightly open the secondary blades or drill small holes in the primary blades to allow more air flow with less opening.

There are a number of HOLLEY tuning manuals around. I suggest you pick one up, read it cover to cover.
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