New chain& sprockets. New rear wheel bearings. New air filter & a little ride around the back yard just to see if it's all ok. Trial tomorrow, no snow here.
Don't forget to earth any ground wires with mild steel fasteners not stainless. As I had this problem with our jtx200. I used stainless thinking that well they wont rust. They don't but they also don't make good conductors. That includes mounting coil etc.
Just have the same problem. The only thing is that when I spray carb cleaner on to the inlet manifold it speeds up. So I am assuming the manifold has a leak. I am having a job to find a replacement. Are there gaskets between the manifold & spacer / reed block? I will try to get it off tomorrow.
My son who is 15 years old rides a 250 pro in competion, has just won a season & has no problem in doing so. He is 5ft 7 & weighs about 8 stone.It' all about set up. every body is different. I ride a 280 & he has no problem with mine either.I think you should go to Gas Gas UK & get in touch with the GURU. You know it makes sense.