Desertrat wins the kewpie doll. Kris^ you are really thinking inside the box man. If the engines in question had specific output where it should be for the money the manufacturers want to charge, a 60cc twin would pull like the 100cc engines they offer now. If that happened all your weight this weight that bull would need quite a rethink wouldn't it? Stop thinking lightest 100cc class motor and start thinking lightest engine that will pull X prop and my notion becomes clearer. When that happens I might think about buying a $1500 purpose built engine but until then I'm sticking to industrial engines where the costs are in line with the performance.