Awhile back, SEARS offered a trimmer that ran on propane, used disposable ' torch ' cylinders . I liked the concept, but never bought one, due to not needing a third trimmer . Seems to me that a lot of the gizmology would be already done, and the displacement of a trimmer would equal some small 4 strokes . Cripes, a smooth throttle, easy starting, long engine life, never clean another carb [ at least not on the bike ] and all the brain busting done for you . Would like to see more done, wasn't the whole idea [ in Massachusetts ] to explore alternative methods of transportation, with cleaner air being a spin off benefit ? In my senile old opinion, all the green movement did was make red tape .