Motorcycle Repair: Overheating Honda NSR 125 RL 1991, honda nsr 125, oil age

Question
Hi Chris,
My brother has the above 125 bike and ever since he got it, it overheats after a few miles on the road. He's got new rings, new engine head, checked radiator and all pipes to see they're not blocked... any ideas.  

Answer
Hey Beavis.
 What coolant mix is he using and what temperature range is he operating in?  Those are both factors in overheating as is the water pump.  Is that working correctly?

Another factor in the heat equation is the oil age and grade.  Are you using an oil grade that has a high heat range?  If you are using 10W40, then it may be too cold an oil to use.  You may need 20W50 oil or the oil in there is too old to work correctly.  If so, then change the oil filter as well.

Normally, the owners manual and the repair manual show the coolant mixture for a given temperature range.  Use that chart.

Check those out and let me know what happens.
Good luck.
FALCON