HI Guys, I'm new to this but I'll try to swim my way around amongst fellow rodders.
Question I have a 600 holley that refuses to idle smoothly. Right now the needles are only open 1/4 turn. Fuel level is at site level plug, I can shut off both needles and engine won't die. Once off Idle and driving engine runs fine. Idle ports are clear, and needles are not damaged. Also hesatates on throttle opening but accelerator pump is squirting a good shot. I have tried to adjust needles open more but even at 1/4 turn seems rich, yes choke is wide open during all this. I was using a Carter AFB prior to the Holley and it was fine. What ever is messing this up I would say it's something in the idle circuit, BUT WHAT IS LEFT?? This is on a 400sbc which has 6000 miles so it is very healthy. Thanks Harry

The first thing that comes to mind is that the throttle position isn't set correctly. You want the transition slots to look like small squares on the primary side. Then adjust the secondaries to achieve proper idle speed.

The transition slots can be seen on the bottom side of the carb. They are the thin slots under the throttle blades. If you adjust the idle screw on the primaries you can get the slots to look like squares.

To adjust the secondary idle setting you may need to take the carb off. This could take a while to finally get the right idle speed, but you will end up with the absolute best possible idle, and transition to cruise. Just remember to use some oil to loosen the secondary idle screw before cranking on it.

A 600 is pretty small for a 400. You may want to consider a larger carb in the near future.

Thanks IIuciano 77, I know exactly what your talking about. I will try that out. 600 little small, yes but this is a stocker daily driver,that with the Carter delivered me 19 MPG (O.D.) of course.
Harry