When the engine revs are high it runs well, the air adjuster screw is set at recommended setting (1.5 turns) and at low rpms the engine sputters out, but isn't flooding. I've tried a replacement carb and it runs fine, so the problem is within the carb.
I've tried opening the air adjuster screw, no effect. I replaced the upper half of the carb with part of another, and the problem is definitely in the lower part of the carb (the part that bolts on the intake manifold, where the air mixture screw and butterfly valve is.)
Thanks for any help / suggestions.