Large rpm drop

Charlesvolare said

Here's where I'm at:
Pulled the carb, lots of transfer slot exposed. Squared it up, figured out how many turns from 0.020" to 0.040".

Put it back on the car, fiddled around to keep it running. Transfer slot at 0.040" secondaries barely cracked open timing at 30*, idle mixture screws 1 turn out from seated, fuel pressure at 6psi, float level checked, 14-15 inhg on vacuum gauge plugged into full manifold vacuum. ~600 rpm in neutral, ~450 in gear, nothing higher. Black, rich smoke in exhaust, enough to fog surrounding neighbors.

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Whoever suggested to take a look at make sure the power valve isn't hitting the boss in the main body is a good idea. Many of them hit that boss, and it will allow a big fuel leak that will drive you nuts.

If that is not the case, the next thing to look at is the Idle Feed Restriction in the metering block.

I looked at a 750 Holley a few weeks ago that had HUGE (and by HUGE I mean MASSIVE) IFR's in it. They measured with pin gauges at .060 and they should be .035-.037ish. So almost double the correct size.

If you have 4 corner idle, you need to verify both metering blocks for IFR.

If you find they are sized wrong, you can use brass set screws to correct that.

Also verify the Idle Air Bleed sizing.