in short- how do i know what size bing carb i have and given that, should i go for a larger one or just lean out jetting?
the long version:
the last owner of my Puch put a 70cc kit on- and I believe either changed the carb to a 15mm bing or kept it the stock size. point is even without an air filter and with a jet that should be too lean for this kit (72) its still 4 stroking throughout the rev range and then full on bogging at top end.
i have good strong spark and ignition timing set to 15 degrees advance (slightly retarded to stop knock, plug gapped to spec, et cetera. does not even start on choke and needs throttle stop screw all the way in. i swear it must be my carb just not being quite big enough to move the air required. from what i hear the OD on the outlet and inlet ports on the 12, 14, and 15mm bings are the same (mine was 20mm). i digress.