siezed, but why?

[Eyedoc]

I siezed up my 92 KDX250 yesterday. I think it may be the water pump. How do I test for this? The gas/oil was ok. Plug was not quite mocha but more an ashen grey color.

Thanks
Ralph, Michigan

 

[David Trustrum]

Lean
Check for airleaks. Your main jet may be too small, it may be partially blocked. Were you using the same gas as usual or was it more than a couple of months old? Had you been running the thing full open throttle where you usually do forest & hadn’t had problems with it being lean?

Small possibility of the ignition timing being too advanced, but that would leave the plug covered in Aluminium & a pit in the top of the piston.

As for the waterpump the simple way to check it is take the cover off it, kick it over & see if it turns. Unlikely to fail.