another good idea is to check the exhaust. an exhaust thats clogged with grime/oil/carbon can slow down the moped alot. i had just cleaned mine out ( i have a motobecane 50v) and its alot better now that its clean. what i did was i sprayed the inside if the exhaust ( after removing the exhaust cap and baffles) with brake cleaner then let it sit for a while (over night would be best and put it in a bucket of some sort because it can really make a mess). let it dry then reassemble and attach.