I think I have mentioned this before ... but these carbies on the siamese bore models have a habit of running rich.... In my many frustratiing hours of stuffing around I have discovered that: If you increase the main air bleed jet hole size ( the brass screw in thing called the air correction jet ,that sits on top of the emulsion tube as you look into the top of the carby ) by around %20 .. it does make a big difference . The factory did this mod. when the spread bore motor was released in 1955 ??

MIKE