I recently purchased a used Chinese 70cc Pit Bike. The oil is quite dirty and I would like to change it. Should I also change/clean the oil filter? I believe this is a Lifan 70cc engine which means I have to remove the cover on the right-side of the engine to access it from what I understand. A google search also shows that it should be filled with 10w-40 motorcycle oil (non-synthetic). I have some 10w-40 (or 30) Amsoil full synthetic on hand. I'm guessing I shouldn't use that? Note: Does anybody have a generic manual for these bikes I could use to reference for maintenance? All recommendations welcome!