Ok, here's my second "I don't know" for the month. I just replace my Holley 750DP with a 850DP. My 750 didn't have the mixture screws for the back and my 850 does. How are the back mixture screws supposed to be adjusted?

1/2 turn is usually close on a 4 sided idle circuit.

I need the same info.i still don't know what or how the mixture screw help on the back side of the carb.(4 corner mixture scews) :confused:

All Holley 4bbls have a secondary idle circuit. Normally it isn't adjustable the ones with 4 idle screws allow you to adjust the secondary idle circuit along with the primary. On an engine with a big cam it can help make tuning easier.

First check and correct timing, then begin tuning of carb. Adjust float levels front and rear till fuel just slightly leaks out port with engine running! Shut off engine, turn clockwise each mixture screw in till it just seats, then back each mixture out (counter-clockwise) 1.5 turns for a starting point. Restart engine, begin with primary, turning in till idle slows, then back out till highest idle, repeat on secondary the same way. Will have to adjust idle up a bit so engine won't stall, go over this procedure several times to get smoothest idle, then readjust idle speed to your preference. This is the way I tune my BBC race motor. Can also set mixture screws with highest vacuum with gage! Hope this helps! :D

yes, that what I thought. I've done it hundreds of times but never on a 4 corner idle circut.