Johnson 25 1979. Shuttering at high RMP.

Hi I just bought this motor. It starts great. But at the last 20 percent of throttle the engine revs funny and shutters and shakes. Also at the lowest end of the throttle it dies. But everything in between is fine.

The guy who sold it to me said he recently installed a carb kit and ran fine before I got it. I bought new fuel tank and fuel line. My mix is good

Anyone have any thoughts?

Thanks

Check gear oil.---Check flywheel key.---The trouble shooting on an outboard starts with a compression test.-----Post your numbers.----You did install a new impeller for water pump I hope.

I have taken some videos of boat motor running. there are now two issues. I also screwed up the year its 1985

1. motor revs wierd and shutters at high rpms https://youtu.be/pffMJkmnQdM

2. motor coughs and sputters leaving high rpms https://youtu.be/gWMydxXU-0Y

thank you everybody

racerone said:

Check gear oil.---Check flywheel key.---The trouble shooting on an outboard starts with a compression test.-----Post your numbers.----You did install a new impeller for water pump I hope.

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I've done compression test : 120 psi both cylinders
I've had the carb professional rebuilt , cleaned with a sonic cleaner
Next thing is fuel pump , but it's pumping fuel .

The spark plugs are soaked in fuel when I pull them

The carb sync: the butterfly starts to open right between marks in the cam

The next thing is timing, but I don't know how to do that yet

My impeller is circulating water very well. Although the engine doesn't warm up. It's cold to touch and water comming out is cold. I'm in very cold water in the Yukon. But I feel like it should have some warmth to it.

Also my slow speed adjustment screw doesn't seem to make any difference in the engine performance. I've gone through adjustment scenario many times

Thanks

Install a new thermostat.

racerone said:

Install a new thermostat.

Click to expand...

Thanks , I've ordered one and gaskets.

I was wondering if you had a look at my videos I have posted earlier in thread? Any thoughts?



Thanks

The thought that comes to my mind after watching the high speed stutter is that the prop hub is slipping.

Hook up a timing light to #1 cylinder.-----Roar down the lake while observing the light.---------Hook up timing light to #2 cylinder.----Roar down the lake while observing the light.-----Report what you observe.

.

My engine is not a 79 its 85. Model J25RWOS

I have just noticed that there is exhaust leaking from exhaust housing cover plate on leg of engine. Is this a serious problem?

That cover plate is there to disconnect the shift rod.-----A leak there does makes more noise.------Does not cause the problem you are having !!---Just replace the gasket.