I don't know all the specifics because it's not mine, but the owner replaced the piston because it burned down. They replaced piston and honed cylinder and said it would run but it would also backfire. This is when I entered the picture and said to them you are lean. I had similar problems a long time ago when I had my '79 Scorpions. When I resurrected them in the early '90s I ended up burning the motor down and after rebuilding, I found a source who told me the carb needed to be rejetted due to the difference in todays fuels compared to when they were made. The Scorpion was stock with a 180 jet and it now runs perfectly with a 200. Anything else you need to know, I can make a call to the owner and get back to you. Thanks again.