I have a 95 400 Scrambler that is .040 over with a fresh rebuild. After about 15-20min of riding it will severly over heat. When the motor was apart I shimmed the water pump and I am getting good flow. I have a pipe clutch and a 260 jet, which is what the manufacture called for. It seams to be running lean. I ran 93 octane. It runs great, but will just get hot to the point it dies! This is the same thing that caused the first motor to go. The head was milled .005 and the cylinder .001 just to make sure they were 100% true. I have Polars gaskets on it. I have great compression the fan works, but it runs hot. Any ideas to help me out I am at a lost! Thanks

 

Did you bleed the cooling system?

 

You sure the thermostat is in correct? If you are have you checked it to make sure its not air bound? Did you also make sure your radiator is free of mud in between the cooling fins? Also you sure your thermostat is working properly? Just because one is new does not make it work correctly, if it is new and you feel that its not air bound I'd pull it and boil it and make sure it opens and closes, its the only sure way it works correctly.

 

The cooling system is fully bled and does not seem to have any air in the system at all. As far as a thermastat the 400 does not use one it is a constant flow system. Any other ideas? Thanks