blue header
 

just the #1 cylinder header pipe is turning blue, it it cracked inside?

Either that cylinder is going lean or the water flow is restricted in that area. The lean condition is most likely caused by a bad injector. The blockage could be from silt or sand lodged inside not allowing water to cool that area. I would start with the injector first. Don't use boat until you get it checked. If it is an injector, you are also causing serious damage to the piston and cylinder.


Smitty

fixx
 

seens it would be easier to pull the hose rack off and see if the header tube is clogged first..

do both, but smitty is making sure he doesn't hurt the engine.

Do you have closed cooling? On my 525's, No. 1 is the last header to get flow. When was the last time you replaces the impellor?