Help Needed, Johnson 35 HP

[Jimmy Jig]

Got a l999 Johnson, 35 HP, 3 cylinder. Took it out this week for some walleyes.
Run good for a time, then the SLOW cut in when motor got to around 2300 RPM.
Would work alright after shuting off for afew minutes, but it keep doing it. The pee stream was good, motor didn't appear to be over heated. Finally unhooked the temp. switch wires and it ran fine for 2 days. Does this switch fail to work right at times? What do you think??? I'm sure the motor was not over heating, I would know it after running at full speed for afew minutes. I see the switch can be tested, hot water must not work for the test, hot oil looks like trouble. Maybe I should buy a new switch and hope that will cure it??

[RUSTY63]

I would be sure that the motor was NOT OVERHEATING, are you using the oil mixer on that motor or do you premix?

[Jimmy Jig]

I still have the oil mixer on it. Its coming off before running it again. I would have removed it before going but the weather has been very cold around here. I see what you are saying about the oil mix, it is taking oil out of the bottle, I burned about 6-1/2 gallons of gas and the oil is somewhere about a pint lower. It always started this trouble after throttling up after idling for 10 to 20 mins. It did not do it when running a higher speeds. Maybe its not getting enough oil at idle speed?? I will take care of the the mixer and mix the oil at 50-1. Would those heat sticks tell the story on the head?? It would be pretty easy to test when operatoring the boat.