I recently installed a 49cc 4-stroke china kit on my bike, it seems like I was really revving just to go 15mph. I opened the transmission and I have 7 teeth on the primary and 41 on the secondary. On the output shaft its 10 and then the rear wheel is 44. By my calculations, that means 5000 rpm=15mph. Did they change the gearing on these transmissions for some reason? Even if I put a 32 tooth sprocket on the rear, 5000 will only get me 20mph. Maybe I should find a larger sprocket for the output shaft? Any suggestions?