My 2000 500 manual just started a new problem. Idles, starts fine
but at 3/4 to wot it starts missing and sputtering. It has never
been drowned and when I fill the bike with gas I always strain the fuel.The bike has 550 miles on it. Would adjusting the valves take care of this problem or is it something in the carb?

 

Sounds like the main jet in the carb is off. Did you change altitudes recently?

 

I bet you have crap in your carb. My 2000 did the same thing about a year ago, turned out it was a brass shaving stuck through the main jet. Cleaned the carb and it ran fine after that. It took around 800 miles for that brass shaving to end up in the jet, go figure. Aczr2k

 

Thank you everyone for your help. I put an inline clear filter inline
and it soon turned a muddy brown color. I took the carb off and disassembled. I discovered the inlet screen on the the carb almost
completely clogged with fine rust powder. I performed this procedure
3 more times and finally took the tank off and fuel shut off and
drained the entire tank. When I hit the reserve portion off the tank
I was shocked to see a thick rust colored mud draining from the outlet
holes on the tank. My next question was where did this come from?
I looked at the gas cap dipstick assembly and discovered rust granuals
on the metal portion of the dipstick guides. After 2 1/2 years of use
snowplowing, mudding, etc the accumulation of condensation on the bare
metal parts of the gas cap fuel guage promoted enough rust to plug the
carb. Why is the fuel guage gas cap not made of plastic when everything
else these days are made of plastic? Well everything is working now and
I am looking to coat the bare steel of the gas guage guides with some
fuel resistant coating. Once again thank you for the assistance and if
anybody else has problems with their carbs maybe my dilema with help them
out.
P.S. i am going to add isopropyl more often to absorb excess condensation.