Johnson 25 horse 1975 model 25R758

by Henry Sherrill
(Waterford Mi)

Hello all. I bought this 25 horse recently for my fishing boat. It is a 1975 Johnson. Starts and runs great the first day reaching 21 mph. The next weekend starts and runs fine in the morning then when it is time to go it will not run wide open throttle. Runs about 5.6 mph. The person who sold me the motor said watch for line collapse the tank is in the front of the boat so I changed the rubber fuel line to copper half inch O.D. added a clear fuel filter. Next weekend same thing runs fine in the morning then runs about the same speed 5.6 mph again in the after noon will not go past this speed. I also changed to rec fuel and Lucas outboard oil mix. Pumping water fine clean fresh fuel. Took it out another weekend same issue and about the same speed 5.6 mph. Which I think is strange almost like it is governed to that speed idle is fine still. Any ideas?

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Sep 08, 2021
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starstarstarstarstar 		filter
by: Henry

I checked it has no filter in that piece. There si a screen that is at the bottom of the pick up tube. Thanks anyway
Sep 08, 2021
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starstarstarstarstar 		Possible cure
by: Kevin

Hi, I had this problem years ago. If the fuel primer ball is still collapsing, check for a clogged screen at the fuel tank line. My fuel tank had a 90 degree antisiphon fitting at the top of the tank. I disconnected the rubber line, removed the fitting from the tank, and below the fitting was a screen that was all but completely clogged restricting fuel flow. I suggest removing the screen altogether, since you now have an accessible filter installed. Hope this helps, good luck

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