Checked ignition timing today and was spot on. Took the air filter top off and found out that if I push the air flap up at the metering head whilst throttling At the engine I can get it to rev and run sweet as a nut so iam now looking along the lines of it being the metering head.. How do these work off the throttle being mechanical injection do the work of vacuum or something? Also there's a breather pipe from the rocker cover to the plenium chamber which squashes flat when running don't think this should do this