Hi all, I just built my first bike and have made quite a few modifications. To start, its a regular Chinese girl with hd lightning coil, sbp expansion chamber, puch 70cc head, ported cylinder, and dellorto 16.16 carburetor running on 100 octane fuel all stuffed into a walmart 29'er genesis. Believe it or not I ride this bike to work everyday thats about a 10 mile round trip and even though I love this bike I'm scared of something going wrong because of the cheap construction quality of the bike and motor. Im thinking about building another bike with a sturdy steel frame then throwing in a 4 stroke of some kind. I want to throw in a racing engine like whats in a dirt kart or similar. I saw a briggs and stratton animal engine the other day at my small engine repair shop and thought it looked the part of what I want. I still want a fast bike (30-35 cruising and 40+ top speed) but I would also like to be able to fill up with pump gas and have an engine i know won't leave me pedaling to work. What is a good engine to start that will fill that role and how can i make it work(i.e. mounting, gear reduction, and so forth)? Sincerely, Cole