I am not sure if you have been asked this yet, but are you running any kind of race fuel or additive in your fuel? No, just 93 octane from the local pump up the road. Here's the thing though. My son has an '01 YZ426 and we ride together in the same conditions (not that dusty) and using the same gas can so it's gotta be something that's failed recently on just my bike. I'm changing out all my vent lines next and I'll post back with results from my next ride.