Does it feel like it has compression when you crank it? Sometimes rings have burrs on the edges but, I’d suspect a fuel flow problem. Trace the pulse passage. Did you get the cylinder base gasket on right? Maybe a crank seal popped out, it happens. Do you hear a good base pop when you crank it with the spark plug out?
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience