Re: ignition timing adjustment methods
It looks to me the timing is set for a good compromise between starting and running. There's no sign of kickback when starting and the engine will run up to reasonable rpms under load. It is possible to improve the engine and get a lot more performance out of it, but there's no free lunch. If you want the bike for reliable long term use the engine is pretty well set up as it is though a bit of cleaning up it's breathing wouldn't hurt. If the compression is raised by shaving the head, re-jetting and running a tuned exhaust the engine will definitely perform better at the high rpm end but that will reduce it's useful life. Higher heat and stress of higher power isn't going to make them last very long. That's without even considering the wisdom of riding at much higher speeds on a bicycle with barely adequate brakes. I don't mind peg scraping on curves and pushing my motorcycles to the limits of my ability but I don't think that's all that great of an idea on a motorized bicycle. The wheels, bearings, tires and brakes just aren't up to a lot of high speed riding.
Goldwing 1500, Silverwing 600, Schwinn 49