2002 WR426 breaks up at WOT

Just picked up a 02 WR426 did an oil change and replaced gas. Bike idles fine and no problems starting. Good throttle response but when I go to WOT the bike breaks up, similar to what happens with a two stroke when the main jet is too small. The bike is missing the airbox lid and muffler baffle and had the stock main jet so I thought it may be lean and tried a few different sizes but don't think that is it since there is no change. One thing I did notice is that the idle adjustment screw will only change the idle when the cold choke is used. When the chokes are not used and the engine is hot the adjustment screw does nothing. Not sure if the two are related and any suggestions what to check?

If it's throttle position dependent, it's certainly carb-related, if it's rpm dependant, electricity might be in question. Try to rev it in neutral and look for missfires on top range of revs. I've got 01 426, with no airbox lid and whole rear part of muffler, went to 170 main, happy as a fck. Good luck.

Looked at the carb and it was missing the slide stop screw. After getting another screw and putting it in the problem is not as bad and think I may be hitting the rev limiter. I have had 2 strokes before and when they ran right the motor would sing at WOT. I guess I am just not familiar with how the 4 stroke should sound. I hope the weather gets dry so my kids can get out and ride!!!

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