Yamaha Blaster Revs up after warmed up

I have a 99 Yamaha Blaster that runs fine until it is warmed up. Once it is warmed up, the engine revs way up when you put the cluch in. Wondering how I can fix this.  

sounds like the pilot jet is clogged up

with the choke on the engine will get more gas,
once it is warmed up and the choke is off if the pilot jet is clogged it can rev out of control.

this is caused by the cylinder getting too little gas and the piston rings becoming red hot, the air in the combustion chamber is hotter and the fuel burns at a different rate.

this is called preignition also, the fuel is igniting because the rings are red hot and not because the spark plug is firing.

remove the carburetor and clean out the jets using a wire bread tie with the plastic coating melted off.
simply blowing them out sometimes won't get the job done.

it could also be the over-rev switches malfunctioning.
but check the carburetor first.  

if you are close to the chattanooga tennessee area bring it by and i'll get it worked out for you.  

Could be air leakage through your crank seals. Once warmed up in 2 strokes with bad crank seals it can leak air into the combustion chamber causing high revs