We have a 2000 sp500 that has just started to backfire very bad. We have been riding the bike for about a month and it has just started. At idle it runs fine but with any throttle it sputters and backfires. WOT it will die out. This is in gear or in neutral. Whats up?

 

sounds like a possible camshaft problem

 

Definitely sounds like a possible camshaft problem. Just had the exhaust lobe on my camshaft go out on my 1999 SP500 last month.
Acted the same way, sounded fine a idle but at about half throttle would cough & sputter and no power. I had a local mechanic do the work and we replaced the camshaft & rocker arms about $350 for the parts and he charged me $200 for the labor. I'm afraid what it would of cost going to a dealership for the fix. Hope that's not what your problem is though but sounds pretty familiar. Good luck.

 

Throttle cabel adjustment on the right dide of the handle bars (ETC).

 

do you have trouble keeping your battery charged?