I got my 30cc Homelite line trimmer engine the same way. I haven't tried to start it yet and won't until I diassemble it, check stuff out and then I'm going to convert it to a boat outboard motor. There are tons of good motorcycle engines out there. Problem #1 you can't use the carb if your plane will fly up, down, left, right or inverted. You'll have to investigate a diaphram type carb. In most cases you'll have to remove the transmission from the engine crankcase. Now, if you can locate an old Norton 750, Triumph 650, Harley 1200 the job is done for you. Why don't you just gravitate to ultra light aircraft? You'd save a ton of money on radio systems.
Bill