ok sorry if this has been covered before but i just got a 05 ds650x and it has a k&n air filter and a fmf slip on exhaust. the person i got it from did not even own tools so i don't think it has been re jetted or any carb mods/adjustments at all have been made. it starts easy (no choke), idles, and runs fine but after about 5min the fan comes on and does not shut off until i kill the motor. i ordered a moose jet kit for it. but when i called the dealer to ask what they would charge to install it they told me that if it doesn't pop,bang, or backfire then my problem is with the cooling system not fuel. they also told me that its normal to not rejet the carb when installing the bolt ons mentioned above but most people say different in things i read online. the cooling system seems to be fine also. i have checked the coolant and its clean,green,and full. the thermostat works fine. should i rejet the carb? is it possible that the stock settings would be fine when there is more airflow?

 

I have removed the airbox, added foam air filter, and added a freeflowing endcap to the stock muffler. I had to jet up from a 165 to a 175 to get it to run well. I also run radiator scoops. Out here in the HOT AZ summers, as long as I am moving forward without overloading the engine, the fan does NOT run all of the time.

I would spend the money to play around with jets. Possibly running your engine lean to the point of running hot is not a good idea.

You might have cooling problems as well. When was it last changed? I run a 50/50 water green coolant mix with the recommended amount of Water Wetter.