Johnson Overheating High Speed

[1988 Johnson 120]

I have a 1988 Johnson 120 HP, new water pump and thermostats, only overheats around 40000 rpm after about a mile of running. Great water flow from water pump even as alarms going off.
Any suggestions?
Thanks

 

[racerone]

40000 RPM sounds wrong.------Check compression as a blown head gasket can cause issues.

 

[Lightwin 3]

I think 4000 RPM's.

Are the water jacket poppets stuck closed. They are under the head inspection covers.

 

[Sea Rider]

How do you know is overheating and how high is the detected temp ? Does OB counts with temp sensors that triggers when detecting an overheat reducing rpm to safe lower ones ? If counting with one, could be already shot, If doesn't count with such sensors, water passages must be full of salt layers, crust reducing cooling effect of passing water through entire powerhead no matter if stats are brand new.

Happy Boating

 

[Faztbullet]

Is the water valve on throttle working??? This is what allows poppets to work.