hi i just finished my 6th motorized bike, all of them have used similar 66cc engines. This engine is an F80 66cc ( 3rd one i have had) they are not the best quality i know lol but i run them through 40 tooth sprockets and with the baffles removed from the exhaust. they all do around 46 to 51 kph. except for this new one with the same setup as previous i only do 38 kph.... I have used other new carbies and still have the same problem. The engine just finished the 500ks run in period and has awesome compression. please help me with any tips at all, thanks josh?