I just got a 1988 ex500 and it ran fine for a couple of days. Then it wouldnt start. I changed the spark plugs and that wasnt it so I opened it up and checked the valves and noticed they were way off and i cant figure out how to adjust it. I pretty sure that this is my problem.

 

DON'T screw with the cam-timing!
If it was running fine at one point, the cam-timing is properly set and there's something else wrong.

Improper cam timing (even if it's only off by one tooth of the cam sprocket) will probably cause the valves to collide with the pistons, which can bend the valves, dent the pistons, and possibly turn your engine into a 180-pound paperweight.

There are two different marks on the rotor that appear through the timing inspection hole--one is the ignition mark and the other is TDC. Since spark ignition actually occurs a few degrees before TDC, you want to use the second mark for checking your cam-placement. Make absolutely certain your using the correct one; but really, if the bike were running fine before, this is almost certainly not the problem!

Good luck diagnosing the problem and let us know how it goes.
-CCinC

P.S. I would ask the seller of this bike WTF is going on. That it was running fine immediately after you bought the bike, but has since deteriorated... smells su****ious.

P.P.S. How long are you warming up the engine? If you let it idle for more than a minute with the choke on, you are probably fouling plugs.