I was looking for a new string trimmer, when I noticed that the 'latest and greatest' idea for weed whackers is a four stroke motor. The vendors make all kinds of claims such as less noise and smog and more power. Has anybody out there used one? Any drawbacks, aside from the engine being more complex? I know 2 strokes don't have valves in the traditional sense, so the four stroke probably has timing gears, a camshaft and pushrods (or are they side valve, or overhead cam?). Probably almost as hard to rebuild as a motorcycle engine. Would accidentally adding 2 stroke oil to the gas cause any problems aside from smoking?