Oh my. I've never had a bike that seemed to be affected to such extremes by the purity or dirtiness of the air filter. My 2015 Yamaha XT 250 is like two completely different bikes. When the filter gets dirty (which it does very easily, being a small paper filter), the XT feels like it's pushing about 19 horsepower. Knock all the dirt and foxtails out, and vaccum the filter clean enough to eat off of, and it jumps right back up to about 23 horsepower. When it's dirty, the bike barely wants to do lame ass wheelies in first gear. Just after cleaning it, the bike will again do pretty snappy second gear power wheelies, with quick pickup and good duration. Finally, when it's dirty, it'll barely hold 55 mph up a section of road near my house, and it won't hold fifth gear at all on the steeper parts of the mountain pass roads around here; when it's nice and clean, however, it has no problem holding 60 or 65 mph up that same section of road, and no problem holding any speed between 35 and 50 mph (or a bit more if I want to) in top gear, on the steepest parts of the mountain-pass roads. That's how much of a difference some dirt in the air filter makes - amazing!