hello i have a 2007 yfz 450 and after i let it sit over night the front brakes lock up and i dont know why but as soon as i open the bleeder valve on one of the calipers it works fine. i hate not being able to just run out and jump on it and ride. any help would be very good.

That's pretty weird. Is it possible you put the wrong kind of break fluid in it and the seals are swelling? Maybe your break fluid has been contaminated. I would start by flushing the whole system and put in fresh fluid. Do the brakes otherwise act normal when your riding? Could be, but I doubt a caliper starting cease up.

i agree, drain the fluid, but take the slides on the calipers apart and grease them, then re bleed some new fluid in.

when i did try to compress the pistons on the caliper they wouldnt if i compressed on the other would push out and i dont know if that might be the problem there something to do with the fluid not being able to flow back up to the res.

might be, could need a rebuild on your master cylinder, or like said above, could be a sign of the wrong fluid, but still, i dont see what would make it close up while it is sitting...