I know of only one plane that has a pull start engine, the Kyosho ducted fan ARF model. But it uses a .15 size engine so it is pretty small, plus there is no prop. And you must realize that a weed-eater doesn't have the large prop disk in front either. Plus a pull start tends to add lots of weight. If you for example have a 30cc engine like your weed-eater has, have you seen the size of the pull start for them? Pretty big, so must also be 1.) Heavy and 2.) Bulky. Therefore you would be putting useless weight in the nose which you could avoid as well as having issues with fitting in the provided space. Furthermore many trucks and cars don't have pull-starts at all because it once again is heavy, and can sometimes even cause air leaks in the backplate due to worn bushing/seal.