94 Johnson 150 after 10 minutes starts to run poorly

[Riverrat8428]

My cousin has a 6 cylinder Johnny that after 10 minutes he describes the motor seems to begin running on half the cylinders. He has taken a compression test and all cylinders are the same. He does not notice any warning horns or other clues. The boat has a built in fuel tank. Have we heard of this before?. Local dealer wants $5000.00 to rebuild the power head. If it will run 10 minutes it should run for ever don't you think/

 

[CATransplant]

Re: 94 Johnson 150 after 10 minutes starts to run poorly

Could be a heat-related failure of some ignition component. That's what it sounds like to me. Not real easy to track down, but lots cheaper than an engine overhaul.

 

[ezeke]

Re: 94 Johnson 150 after 10 minutes starts to run poorly

If you use an inductive timing light while running, you can "see" which cylinders are not firing. Check the shift assist switch if they are all on one side. Be careful running with the cover off.

 

[Riverrat8428]

Re: 94 Johnson 150 after 10 minutes starts to run poorly

Is there one componet sensitive to heat that might be the culprit? The timing light is a good trick and we will try this..

 

[tashasdaddy]

Re: 94 Johnson 150 after 10 minutes starts to run poorly

there are several, coils, power pack, stator. hopefully it is just a coil.

 

[Chris1956]

Re: 94 Johnson 150 after 10 minutes starts to run poorly

The heat temp sensor on that motor may cause the powerpack to kill spark to 1/2 the motor. While it is running put your hand on the heads and see if it is overheating. If you can hold your hand on the head after 10 minutes, disconnect the temp sensors (one on each head) and see if the problem goes away. if so, ohm out the sensors. the one that is shorted to ground is bad.

 

[Riverrat8428]

Re: 94 Johnson 150 after 10 minutes starts to run poorly

Weve got some snow falling right this minute however as soon as possible you have given us a direction to head thanks.. When we find it I'll pass the findings along..