My Brothers 2003 WR450F with only 2000 miles on it is starting to miss at midrange and its really difficult to start.. I don't know much about yamaha thumpers, and hoping someone can point me in the right direction... He's got an owners manual, and I suggested we do a valve check and clean the carb to start... The fork seal is different than my DRZ400 because its inverted - maybe someone can explain the difference - should be simple... Do these bikes have valve problems or could it be simply that its jetted for the desert and just ran funny at the beaches in Baja?? I assume the fuel screw is accessable, or does the plug need to be drilled out? Thanks.