I've got a HuaSheng 142F 4 Stroke with a 44t sprocket, 26 inch wheel and an NGK plug. The rest of the engine is stock and no real modifications have been made to it. This has been an issue since the day I got the bike, 6 months ago. The bike takes off great and hits 19-20 mph with no issue at all. It's torque is perfect but when I reach my 20mph, I'm at about 1/2 throttle. If I try to go any higher on the throttle, it'll feels like it chokes up. In other words, it refuses to redline. I've seen these bikes do 25 mph easily with no changes, so something is wrong. The bike doesn't die out or anything if I exceed that 1/2 throttle, it just sort of chops forward, chokes, and drops me back down to 20, If I try to hold it, i'll feel an occasional jerk forward but it'll always cut back down to a rough 20. Things I have done Valve Adjustment Cleaned the Carb Tried 89 and 91 octane gas Checked Carb Gaskets Cleaned Spark Plug Upgraded Spark Plug (NGK) Cleaned the Air Filter (and removed for testing) Checked Clutch Pads and Clutch Assembly (It's fine) New Fuel Filter Cleaned Float Bowl Things I haven't done, but might try Upgrade Exhaust Pipe Upgrade the Carb / Intake Try a new CDI / Magneto Rotor Drill my Jet Keep in mind, I'm not trying to performance mod this bike yet, I'm just trying to get power that should already be there. I know a good pipe or a good carb might help, but I think this is an issue, not a performance tweak. I read another thread about the CDI limiting RPM's, but I have the non limited CDI in the engine, I checked. In the same thread he mentioned changing his Magneto rotor, but I'm not sure I wanna buy one simply for diagnostics. Appreciate any advice. Thanks.