Stihl
It can be done. I used to race open 2 cycle karts with a guy that quit and started racing rc boats. He started building and selling engines for the boats because he set a few world records with his engines. I use to see him at the city auctions and he said he was looking for a certain stihl weedeater for the engine off of it. I know he was really good at modifying engines and he would change the port timing and could make them fast. That being said I'm not sure how fast they would be stock but it would be worth trying for sure.