Im new to this site and need some help.

I was given a 97 polaris sp 500. It needs alot of work but the price was right. It will start, but it pops and backfires through the carb bad. I checked the valves and also adjusted them. The valves were tight but other then that they looked good. Timing is right and the compression is good. I took the carb apart and noticed someone had JB welded one of the ears the float pin goes through. it looked pretty crooked. Im just looking for any ideas to get this thing running right so I can tackle all the other things wrong with it(RF axle knuckle out, no ignition switch, fenders especially front is bad, tires bad) but again price was right.
Could it be lean fuel, bad spark plug.
I will take any advice.

 

Check for a worn cam lobe, the early 500s were notorious for wearing out the center cam lobe. Buddies was worn completely off and it was doing the same thing.

 

Check the exhaust cam lob. Here is a link about it.

Polaris Camshaft - The Garage Journal Board

 

I know the exhaust valves were opening up, but if the lobe is worn anbd they either are not opening up enough or for long enough would that still cause this problem?
If I replace the cam shaft, I should replace the rocker arms also?
Thanks for the quick replies.