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?