The NSR150SP has reasonable piston, cylinders & heads, but that's about all! The carb is too small, the intake is restrictive, the flywheel is heavy, the balance shaft is not very well balanced and the stock exhaust is heavy and passes less gass than Andy after a night on the razz. You can get up to about 29hp with a pipe. Maybe 30 with a carb as well, but anything after that requires that you go internal and start cutting.