The reason why is a good question alright. AV8TOR has dad very good luck with them. They are lite bcause of no external ignition is needed. Just a Glow plug to start them up. This is mainly done with engines from leaf blowers and chainsaws. They tend to give you more RPM I guess...I think because of some Nitro in the glow fuel that is mixed with gas. It takes some reading to get the idea. With me its a kinda a experimental thing...my main airplanes will be gas. Unless I get some real power with a pipe...but for now its just experimental. Capt,n