2009 450 fsr bogs when hot

[schlitzy]

So the valves went out of spec at about 60 hours. Replaced the valves and set the clearance. The bike now starts very easily when cold. When it gets hot, after about 15-20 minutes, it starts to sputter. It will run if more throttle is added. If it dies it will rarely restart when hot, let it cool and it starts back up and runs great..until it heats up again. Everything on the inside looks great, no leaks and when it is cool the power is great and it sounds great. Any one have any ideas? Compression is good. Are there any sensors which go bad slowly? Would a fuel injector get partially clogged?