Hey, i'm thinking of getting a derbi GPR50. Can anyone give me any information about them? I currently have a Tomos Targa Lx, witha 70cc kit, but only can get to 65 mph downhill. How can stock GPR50s, which are 50cc, and seem to look a lot heavier, do 70 mph? I don't understand. What do they do to the engines, and how can i do that to mine? Thanx