Hi- I'm new to your forum and wanted to post my project from a couple of years back. This bike as had a Riobi engine, a 3hp Briggs, a 5hp Briggs (pictured) and electric on it. The best combo has been the 3hp Briggs. Doesn't shake too much, and it'll still hit 35mph on level ground. I can change gears with the bike's gear-change, but NOT while the engine is running... it shreds the bike chain when I do that! Last picture is of the 3hp.