How hot it too hot?

I recently got back into the dirt bike scene after 20yrs away. I got a good deal on a '99 YZ400F and picked up a TT-R90 for my son to learn on. My question is that since we do a lot of low speed riding, twice the 400 has gotten so hot it's pushed out water through the overflow. This concerns me, but without a gauge, how do I know when I need to run it to cool it off? I really don't want to warp something or blow a gasket...thanks.

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It's possible that your machine is not running too hot. If you fill the radiator to the top of the neck, it will spit out some coolant. Leave about an inch below the neck flange and see if it still discharges coolant. There needs to be a little space for thermal expansion.

remember this bike is a very high compression

race bike,it doesnt want to run at slow speeds and was designed to run at higher speeds.the wr's have the cam either retarded or advanced to for better bottom end.

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