1985 Johnson 8 hp occasionally goes berzerk

[B1gM1ke]

So a typical day on the water motor starts fine, idles good, runs wot fine. Motor will run fine then all of a sudden the motor will near die. I have to throttle down and let it idle and goose the throttle a few times to keep it running. Runs like an engine that has it's wires crossed when this is happenning. Then as fast as it started acting up it goes back to normal and runs fine for the rest of the trip ... I found what I think may be the issue today. Am I correct? Would the issue in the pic cause this issue? Notice the top unit looks melted and over heated while the bottom unit looks smooth. See pics please.

 

[B1gM1ke]

Pretty sure those are the coils I have concerns with...anybody?

 

[racerone]

Yes those are the ignition coils.----But it sounds like a fuel problem.---Start with borrowing another tank and hose as a test.

 

[B1gM1ke]

First off let me thank you for your response. It has a brand new tank and hose on it. At first I thought it was air in the fuel line or water maybe but the last time it acted up it was very much acting like an electrical issue. It doesn't bog down when it acts up it shuts rite off for a second, like someone hit an off switch. Then when I goose it the engine runs very ruff and actually makes what sounds like a backfire which is why I said it runs like an engine with it's wires crossed. When it does go back to running fine it runs pretty good except when slowly throttling up from idle it's not really smooth. Still sound like a fuel issue to you? And what do you think of the coil that appears to have heat damage?

 

[Mohawkmtrs]

Hard to tell from the pictures.

When it acts up, put a timing light on each plug wire to test the coil(s).

 

[Sno]

I have a similar motor that had this behavior. It happened more frequently and after thorough check on usual fuel issues and switching each coil one at a time from another motor that ran reliably it finally resolved when I used the power pack from the other motor. If I hadn't had the other motor, and the parts to switch, I would have had to learn how to properly troubleshoot this type of system. I don't want to derail the thread, but I'd be interested in more from the experts in how to approach this, i.e. I'm not the one to make a suggestion on a next move at this point for you.

 

[boobie]

Do a cylinder drop test on it when it acts up and maybe you'll find something.

 

[B1gM1ke]

It has been suggested that after prolonged idling for trolling I'm losing fuel line/tank pressure. I was told to try pumping the bulb a cpl times to bring up the pressure before throttling up after trolling to see if the issue is solved. Will keep you all posted. And what is a cylinder drop test?

 

[boobie]

Pull a spark plug wire one off at a time when it's acting up and see what cylinder is doing it or both.