I just bought a 2000 400ex and it's giving me a problem with the thumb throttle. The throttle is completely fine when shut off, but only gives me a hard time when riding. When I push it, sometimes it stops at half throttle and I have to press it harder to get it to go the rest of the way. It feels harder and isn't as smooth as I feel it should. It almost always gets caught at half throttle and I have to press it harder to get more throttle out of it.