1986 140 Johnson Overheat and loss of power

mercmafia

Cadet
Joined
Jun 21, 2010
Messages
26
I have a 86 140 Johnson on the back of a 21 foot Chris Craft Scorpion open bow outboard. I pulled the lower last season and replaced the impeller and the housing. Then the first time I took the boat out I was getting an overheat alarm. I removed the thermostats and found that one of them was melted so I removed both of them and put it in the water and still have an overheat. After reading on the forum, I decided to backflush the coolant ports on the head and now this time when I dropped the lower, I noticed that the gasket for the exhaust housing on the upper was ripped and twisted...would this cause an overheat scenario, where water is pushed away from the motor while trying to get up on plane?

And as the loss of power goes, the boat will not get up on plane without the overheat alarm going off. But if I let the motor cool, I can give it throttle and it acts like it is starving for fuel. And if it decides to get up on plane, the motor will deaccelerate very quickly and then sit there and either shut off or begin shaking violently and rev up and down repeataly. I have been told to check the check valve off of the fuel tank but I do not see one. All I see is a shut off valve mounted to the top.
 

pn

Petty Officer 1st Class
Joined
Apr 20, 2013
Messages
374
Re: 1986 140 Johnson Overheat and loss of power

check your compression to see if your motor is not fried. then make sure your motor pees, a dry thermostat is no good. then look at your fuel delivery tank to carbs. good luck
 
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