My front brake on my 08 YZ450 always looses some of its 'compression' while riding. Sometimes the brake pressure will start to come on near the beginning of pulling the lever and other times it wont come on until its almost hitting my knuckles. The actuation point could change from corner to corner. If I pump the lever it hardens up and all is good, but a few corners later the actuation point is too low again. Ive bled the brakes many times and it fixes the problem for a while but it soon returns. Two things which I think could be happening is air bubbles are getting in the line from the top of the master cylinder reservoir while riding, or, bits of dust/dirt getting inbetween the pads and disk and slightly pushing the caliper apart? The disc does not looked to be warped at all. I dont know but does anyone else experience this?