Have you removed the airbox lid?? Do you have a good, clean, oiled air filter?? Sometimes if I'm lazy and haven't cleaned the air filter in a while I can feel it in the throttle response!! Getting the jetting correct will also help, gives you max power and throttle response/acceleration!! If you're stock and still with the oiling system, once you remove the airbox cover and have a good air filter on there you may want to go up on, maybe two sizes on the main and play with the needle a tad, potentially. As with the dirty air filter, when the seasons/temps change I can feel the lack of power/acceleration when the jetting is off.
Also, what makes you think that your top end is on it's way out?? I got my blasters from a friend that had not been good to them, and then they sat outside his parents house under a tarp for 4 years while he was away at college. I got them and immediately ripped the top end apart as he had no airbox cover, fmf, and used to beat the bag out of it with no jetting changes. To my surprise, the piston and cylinder looked brand new and I just ended up honing the cylinder and popping in new rings. My plan was bore and wiseco.
