Alright so i went and tightened up my chain on a 2004 yamaha blaster and now it steers to the right by itself even when i do wheelies i tried to do it again and made sure each side was even but it still does it and its really anoying please help me out thanks  

check your axle bearings.

if the bearings are bad and you tightened the chain it could be pulling the axle at an angle.

the housing would be straight but the axle bearings would allow the axle to move while the housing is tightened down.

an easy way to check these is to put the atv on a jack and grab both wheels and push one wheel foward and pull the other backward.
see if it moves.

if the axle bearings are worn out check out www.rjatv.com  he has a set of axle bearings made by "all balls" that are better than stock.

and his prices are really good.  

Hey i think i know whats wrong... i thought about it and it would turn to the right if the tires had different pressure in the back. when i kick each of em it seems like the right has alot less air than the left... later today im gonna fill them both up even and take it for a ride again