mine does/did the same thing. Finally I got fed up with it and took it to a local performance shop. Not the kind you see when your driving around all flashy and whatnot with Honda's in the parking lot... I mean the kind where the building is the same since it opened in in 1964, same sign and most importantly same mechanics... The owner (Rick of Rick's service garage) worked on it all day, rebuilt the brand new carb and found metal filings in the idle circuit... he also found an exhaust leak. However, the most important reason he told me that it wouldnt idle in gear was because my stock tranny/torque converter were unable to deal with the new torque of the engine at idle and it would drag the rpm down too low for it to continue running with the lumpy cam.
Hope some of that helps...