I have a 1965 t90 with Boyer ignition.Used to misfire at 4000rpm and above, felt as if it was fuel starvation, but maybe not Now Having problems starting. seriousbackfire through exhaust,black plugs,and if/when I get it started it sounds v rough with some popping through exhaust.Fuel getting to carb.good spark.Even if use full chke plugs never wet.Have stripped/cleaned carb.Any ideas. Thanks Neil