CRM 125 Overheating (NSR125 based engine) - any ideas?

[G]

My CRM seems to overheat when riding off road, I haven’t noticed it overheating on road – but I tend to be going faster at lower revs off road. It may be that it has been getting high while road riding, but not enough to piss out steam.
I’ve checked and replaced the coolant recently, though it seems to be ok.

Any ideas on what might be causing this?

I thought I’d ask before I start poking it at the weekend.

My current plan of action is …
Get the head off; want to check the piston/bore anyway.

Flush out the coolant system and replace coolant again.


Could it be a ‘too hot’ rated spark plug?

I installed a 120mm PC fan on the back of the radiator which did seem to help in some cases; however it wasn’t very powerful so I’m thinking one from an SV/RS250/R6 etc that I’ve got sitting around might do a better job. I unplugged the headlight and plugged this into the dip beam plug for the headlight.
(of course it’d be better to sort the actual problem in the first case, presuming there is one)

Any other suggestions?

[NSR Mick]

Knackered thermostat.
____________________
If you dont like the way that I ride.......Stop trying to keep up!!!

[alains]

probably , i agree . easy to check :
- take off the pipe entry on the head and take calorstat out
- put some water in a pan and warm it until it begins to bubble while observing it , if it is not open at 75° C (i do not know how much in farenheit) it's worn
unfortunatly it's not free ! but you can run without it , the only unconvenience : engine takes longer to warm .
also check if the fan you've fit pull the air and not the contrary (changing polarity will reverse the way of turning)
you can change the propellar in the water pump (you need a new seal)
____________________
the worst day fishing is better than the best day working

[G]

Cheers, I had actually had that suggested to me before, but a quick google had suggested this engine didn't have a thermostat.

As it does, that definitely seems to make sense.

Cheers for the thoughts.

[stevo as b4]

You could check the Rad too for silting up, and also damage to the fins, which is quite common on bikes used hard off road. Try backflushing the rad too, and if it looks dented or badly silted up, then just get hold of a new one, as a radiator isn't going to be very expensive for a small trailie anyway!