Running rich....To big of a carb or?

C130 Chief said

I would keep drill bits back in the tool box for a while. First, go buy a vacuum gauge! They're cheap and just about mandatory for carb tuning. As said above, both PV's should be well below idle vacuum (and the secondary should be 2 numbers below the primary). Because you need to nearly seat the idle mix screws, I would concur that the primary jets are too large. Try going down 2 numbers at a time on the primaries until the car slows down, then go back up one number. Best to disable the secondaries, until you have the primaries set right.

If I was a betting man, I'd bet you'll end up with #74 jets, 8.5 PV primary, #77 jets 6.5 PV secondary. Make sure the float levels are right before you monkey with anything else.

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Vacuum carbs don't have secondary power valves. And you may need those fat jets when the rpm's come up. You would not believe the difference the idle air bleeds make in the transition from the idle circuit to High speed. and then the High speed air bleeds from mid to high.

They have metering blocks with replaceable emulsion jets also to really fine tune. But usually if the carb is 750 cfm it calls for a specific size main jet for that carb. The last thing I would change is the mains. Unless you have a wide band rich lean gauge hooked to a o2 sensor .

Changing the idle circuit will not cause Damage to the motor but will lean it up on the bottom.

The only time you need to drill holes in the venturies is when they need to be opened up past the idle transfer slots for it to idle.

The rule of thumb is as much of the slot should be uncovered at idle as the slot is wide. square it up.

on a 4 corner carb you set the primaries at that and then idle off the secondaries. If you take time and do that with a standard Holley you can make a big difference in performance.

If you really don't want the hassel of fine tuning your carb get a Carter style carb. they sort of adjust them selfves better then a holley. They have metering rods. And adjustable spring controlled secondaries