[ted]

If your carb is running rich at idle, you can try several things.

First, screw the idle mixture screws in equally until the engine falters then adjust for best idle or vacuum reading. If the screws go all the way in and the engine is still running, then you're probably pulling fuel from the main circuit which means too much throttle opening. If it's a four idle circuit carb, then the primary and secondary throttle plates should be open evenly. If it's a carb with only primary idle circuits, then you can try cracking open the secondary plates slightly more so that the primary plates can be closed some more. This will put more demand on the primary idle circuit.

Worst case scenario when all else fails, pull the carb and check out how much idle transfer circuit is exposed at the throttle plates. If it's more than 0.040", then additional holes may have to be drilled in the plates so that the throttle plates can be closed off some more thereby allowing idle circuit adjustment.

And before I forget, the simplest and easiest "rich at idle" problem to fix is the power valve. Either its bad or not seated well against its gasket. Usually pulling off the metering plate and looking at the cavity behind the power valve to see if its wet back in there is a good indicator of a problem in this area. If you've got a cam with lots of overlap, this tuning tip probably will not work as it may be wet anyway.

And while we're on the subject of power valves, the power valve could be wrong for your application. If the manifold vacuum is too low, then the power valve is not closing at idle and causing a rich scenario. A vacuum gauge will help out here. You'll want a power valve that is rated at least 1 inch Hg above whatever your manifold vacuum is at idle (and if an automatic trans, in gear).

And....... the list goes on and on.