I have this M that came in the shop and the Guy says tune er up good it doesnt have any power -- OK says I - I put a complete pertronics kit in it and it started and run real nice - I put it on the dyno - got her warmed up good and started putting the coals to her and run good at 45 HP for about 2 minutes and started to backfire out thru the carb -- backed up the dyno and it cleared its self -- no carb adjustment cured it -- checked valve clearance timing and all I know is it must be a stickey intake valve -- now what -- I put sea foam in the gas and the oil -- any other thoughts out there? Roy