99GP12 problem

[99GP12X]

I have 99 gp 12 with 80hrs. i got it used from adealer. I was riding last week for 3-5 hrs and everything was great until the last 15 min it start to make like a backfire or popping noise from the engine it would get above 6500 rpm and 54 mph. i was getting 7000 and 61 before that. Can any one give me some help with what could be wrong any one have this prob.
Thanks,
TOM

[Bryan Glynn]

Take a compression check, then try fresh plugs. Can you tell if the backfire is through the exhaust or intake?

[99GP12X]

Dont Know where the poping is comming from.
I checked the plugs they were a light brown color. Some times it would make the same noise when i first started it but then it would go away i just thought it was warming up.

[99gp1200]

Brian, What is backfiring through the exhaust an indication of. My GP1200 runs like a champ
but occasionally will back fire whan I am blowing the water out of the exhaust after riding.

[Bryan Glynn]

Usually a plug intermittantly firing or too much gas in the exhaust - possibly a carb too rich, or low compression.