A Perry carb is very delicate in it's idle fuel cirquit. Unlike the ST carb, the Perry is not self-cleaning. The internal metering slit is very narrow, and may need some cleaning attention if the carb does not tune well. With carbs like this, the fuel suction line MUST have a super filter (felt clunk etc), and the line must never be disconnected for any reason except dismantling. NO T-fill connection either.