2004 450ES 4000plus kms on it. Went to mountains this weekend and as we proceeded up steep hill quad started missing under load. elevation about 5000feet above sea level. Had never done this before. This went on all morning, had to rev the **** out of it to get up hills and used more fuel than normal. Got back to camp and hubby rejetted the carb a little. It helped and quad performed great. Need to know if this is what a jetting problem really is or is it something worse. Next problem was that all of a sudden reverse would not work. really tough when negotiating bush and trees. Hubby thinks it is the microswitch at the handle bars. Push buttons are not the issue. after some fiddling with that it worked good this morning at camp. Please let me know if you have had similar problem .