Working with a ProForm 600 cfm carb. This is installed on a Chevy 327 with a solid lifter cam and 285/290 duration, advertising I think, and .500 lift or so. Generates 10" of vacuum at idle. I am having problems with the idle circuit, car will run with all four idle mixture screws closed. So thinking I had the throttle blades open too far I removed carb flipped it over and found the secondaries could completely cover the transisition slot, I set the blades to expose .025 of the slot.
Now the primaries are another story. With the blades completely closed I have .080 of the slot exposed, but the car will not run in this position, so it has to be opened even more when running. To me this means the idle circuit on the primaries is not working, hence the problems with mixture screws. I called Proform and they checked another carb and it was the same, but apparently different than one of their other models?
I did check the power valve, several times, I even put a plug in it just for testing purposes. 4.5 power valve installed now.
Anyway, anybody else have this issue? How did you fix it?
Thanks!

 

Check all of the idle circuit passages. Throttle body, main body, metering block, air bleeds. You wouldn't be the first person to get a carb with a passage that wasn't properly machined, cleaned, deburred, etc.