I just bought a 2003 wr 450 and thought the carb needed to be cleaned out. I tore the carb off of it and noticed the side where the throttle cables were was all coroded and nasty. I cleaned it up. The little plastic actuator that works the accel. pump piston was not opening all the way when the the throttle was opened. Could the spring that opens the accel. pump be worn out. I can work the pump manually and it squirts fine. The bike will run with the choke on but when I turn the choke off and crack the throttle quickly the bike dies. My friend said the valves also might need to be adjusted. I do know that the accel. pump is not working properly. The bike has the stock exhaust with the baffle taken out and it backfires and shoots a flame out when reved high. Please help if you have any idea.