Ok so I built a friction drive bike with maybe a 20 or 21cc engine it works fine and the whole build was completely free which I was pretty proud of lol anyway I have been trying to get more power and experimenting with different home made systems right now I have about 3 inches of pipe coming off the stock muffler and I hooked a emptied spray paint can to it and just a few minutes ago added a smaller diameter tip to try to create back pressure I don't know weather to call it an expansion chamber or redneck muffler haha but can't go up hills without doing most of the work with this little and old engine I can't spend reall any money as I am broke and Savin for vacation also I'd like to keep the challenge of completely free going but any advice would be greatly appreciated 
