I agree with Randy and will show my bias. I suggest you find a Honda 70 or 110 model and transplant a BS 90. It would run circles around the Hondas. Sorry, got that out of my system. Sometimes "unsticking" requires desperate measures. Explore the threads on here to see the lengths some members have gone to to free stuck engines. In my case, I have literally resorted to driving the pistons out of the cylinders of a stuck 350, and while it damaged the cylinders, both were repaired and replated and are ready for use in a motor I am building.
...bert