I've been wanting to change the timing,(I'm at 5500 f.a.s.l.) In a car, the higher the altitude you need to advance the timing for the best power/performance. This Thing ran GREAT for two days, then it would not idle. I found an in-take leak. I fixed that and now it runs like it did while break in. Plug is gray not tan like I would like. It is not to rich, but I'd like to lean it out a touch. I'm thinking more towards an exhaust problem. (maybe clogged). I've had a lot of 2 stroke dirt bikes, but never messed with them unless they would not run. Not real sure what to try next? ???? Can any body tell me is the out put shaft (drive sprocket) lubricated by fuel oil mixture or is it a sealed bearing? I have not had one tore down this far yet! So I'm not sure of the inner workings. Break down picts are vague.