Motorcycle Repair: THROTTLE BOGG, air fuel mixture, yamaha raptor 660

Question
I HAVE A QUESTION ABOUT A 2005 YAMAHA RAPTOR 660 I JUST PURCHASED. I BOUGHT THIS ATV 2 DAYS AGO AND RODE IT FOR THE FIRST TIME YESTERDAY. AFTER LESS THEN AN HOUR I STARTED TO HAVE A PROBLEM WITH MY THROTTLE. IF I JUST BARELY TOUCH THE THROTTLE IT STARTS TO BOGG DOWN AND THEN AFTER ABOUT 2 OR 3 MIN IT WILL STALL. IF I START IT AGAIN IT WILL ACT THE SAME AND STALL. IF I ALLOW IT COOL DOWN FOR ABOUT 10-15 MIN IT WILL RUN FINE I CAN REV THE THROTTLE WIDE OPEN WITH NO PROBLEM BUT AFTER IT GETS HOT AGAIN IT STARTS TO ACT UP ONCE AGAIN. THE PROBLEM SEEMS TO GET WORSE AS IT GETS HOTTER. I MEAN, WHEN IT STARTS TO ACT UP ITS AT VERY LIGHT THROTTLE BUT WITH EVERY TRY AFTER THAT IT SEEMS MORE AND MORE WORSE TILL I CANT EVEN GO WIDE OPEN IT JUST WONT STAY ON. THE GUY I PURCHASED THE ATV FROM SAID IT HAS A JET KIT AND IT DOES HAVE A FHM SLIP ON. AS MY OWN PERSONAL RULE OF THUMB WHEN EVER I PURCHASE A NEW ("TO ME") VECHICLE I GIVE IT A FULL TUNE UP. NEW NGK PLUG K&N FILTER, OIL, BRAKES, BOTH PADS AND FLUID CHANGE, COOLANT FLUSH ETC. I DID NOT DO THIS TO TRY TO REPAIR THE PROBLEM JUST SO I KNOW IT HAS BEEN DONE. AS FOR THE PROBLEM I REMOVED THE CARB BOWL'S AND JUST SPRAYED THEM WITH CARB CLEANER. I AM TRYING TO FIND OUT IF I SHOULD TAKE THE CARBS COMPLEATELY APART FOR A CLEANING OR DO YOU THINK AND AIR FUEL MIXTURE ADJ MIGHT DO THE TRICK. THE AIR FILTER IS STILL IN THE AIR BOX HE DID NOT FREMOVE IT NOR WILL I. I ALSO DRAINED OUT ALL THE GAS FROM THE TANK TO RULE OUT BAD GAS CAUSE IT WAS THE FIRST THING THAT CAME TO MIND. THE PROBLEM IS I DONT HAVE NO HISTORY ON THE ATV. THE MAN I BOUGHT IT FROM SOLD IT FOR HIS SON IN THE ARMY. ALL HE TOLD ME IS THAT IT HAS A JET KIT AND IT HAS BEEN RIDDEN BY THE YOUNGER BROTHER. I DID READ ON THE NET THAT THERE WAS A PROBLEM WITH THE EMERGENCY BRAKE FOOLING THE BIKE INTO THINKING IT WAS ON WHEN IT GETS STUCK BUT I AM REALLY LEANING TOWARD THE CARBS. I APPOLIGUIZE THIS WAS SO LONG AND I APPRECIATE YOU HELP. MY EMAIL ADDRESS IS "ALTEREDIMAGES30@HOTMAIL.COM   THANKS AGAIN..

Answer
Hi Mike,

Very good narrative description, thanks.

The carburetors will need thoroughly cleaned and then tuned to correct the air-fuel mixtures (jetting).

If you flushed the cooling system, did you use a purging tool to purge air from the cooling system? If not, this must be done.

The cooling system is designed to be air free. Air enters the system anytime the system is opened to air, with the exception of removing the radiator cap or reservoir cap.

Air lowers the boiling point of coolant to a temperature just above the boiling point of water. Kinda makes coolant useless. If aair is in the cooling system, the engine will easily over-heat or run at high temperatures that may contribute to problems you've described.

Use a tool such as MityVac's "AirEvac" purging tool. This tool is expensive, but this procedure is mandatory.

I would like to send you tech information files to assist you. Do you have another email address? Free email servers such as Hotmail and Yahoo do not receive my large tech files.

Respectfully,
Mark Shively