OS is like Ford, found on road dead. I have an OS 91 piece of junk, and I also have Magnum 91 and Saito 90 plus Magnums and Saitos in other size designations. I have very few problems with my engines but both my OS engines have never started by just flicking the spinner. It always requires use of an electric starter, my Magnums and Saitos start immediately after priming and a slight back flip of the spinners. Even my Magnum 80 out flies the OS 91 both have the same prop and are mounted in like sized and weighted aircraft. Magnums for their price are a very good value and offer way better performance than OS, which in my opinion should be a Yugo. You go get a better engine, buy a Magnum.