I have an 03 636 and an 05 636. When I do standups on my 03 it drifts like a ***** to the right, but when I am on my 05, I do not have this problem. So, could it be caused by the rear tire not being perfectly straight in the swingarm? Or maybe my rear tire is bad?

I just cant seem to figure it out. I even hang off the left side of the bike sometimes and it still drifts right

 

ajust ur chain ajuster to make the wheel point to the right side of the bike, that will put weight on the left side of the bike when ur in a wheelie. see if that helps, make sure to keep proper chain tension.