Have a holley classic double pumper . Bought it new and ran ok on my 402 . recently the engine barely wants to idle ..If im in drive she will die out .. Idle is eratic jumps 1,000-1,200 rpms .. Heres the thing ,I can get it to run (ok ?) if I bottom my idle screws out ? I Changed my disharge nozzles and got rid of my flat spot .Then this all started occuring ? When I am driving at consitant speed the engine surges .. Hard to explain almost as if it missing. I running out of ideas , any thoughts ?

The constant surge at speed is a lean condition,if it didn't do this before check your float level it may be to low.If your fuel level is at the bottom of sight plug then you have dirt or something in the main metering part of carb,you'll have to remove front bowl and metering block and squirt carb cleaner through all the openings don't forget the air bleeds on top of carb.On the idle part of carb it sounds like the throttle blades are open to far and engine is idling off of main circut not idle circut,try backing out the idle speed screw then adjust idle mixture srews usually 1 1/2 turns will put you in the ballpark.

The float level is good . If i back out the mixture screws the engine will die .. Any other ideas ?

JR's right about the idle... Take the carb off and turn it over (empty the bowls first) If it's a 4 corner idle adjust the primary and sec throttle blades so they only uncover about .020" - .030" of the transfer slot in each throttle bore. The slots are .020" wide so use that to judge how far you open the throttle blades. If it only idles on the primaries adjust them and then find the sec throttle blade adjustment screw and back it off until the sec plades are closed all the way but the screw is still touching. Give it a 1/4 to 1/2 turn tighter, no more..

Next set your rich/lean mixture screws all 4 if you have 4 about a turn to a turn and 1/4 out from seated. Bolt that baby back up and fire it up. Check for leaks and when warmed up adjust the rich/lean for most vacuum or highest idle. shut her down and count how far each screw is adjusted and if one is 1 turn and the other is 1 1/4 turns split the difference so all are the same. Fire it back up and set the idle. If 4 corner do both idle screws the same 1/8 turns at a time...

You may need to replace the power valve. It sounds like you are running very rich at idle. If it ran ok before there are not many things that will make it run rich at idle except the power valve. Good luck

Don

When you take it off, tighten up all the screws, particularly the ones on the bottom that go through the baseplate.

You could check for rich condition by pulling a vacuum line off the baseplate - if your idle picks up, Don is likely right on the money.

Have you checked for vaccum leaks? Spray some carb cleaner around the base and see if you notice a difference. You can get sporadic trouble with a loose carb to intake or carb body to baseplate.