Johnson J15RSOC 15HP Issues

[EastTNHunter]

Took my jon boat out yesterday to hunt. On the return trip everything ran just fine for the first couple of miles, but then it started to “bog down” slowly despite the fact that I had the throttle held wide open. I let off the throttle to idle speed for just a few seconds, then opened it back up and she ran fine again for another 1/4 mile or so only to repeat itself over and over until we got back to the boat ramp. Ran fine at idle, no real “hiccups” or misses, and the “bogging down” was as smooth as if I had just let off the tiller throttle slowly. I’m using an inline fuel filter, and I see no major issues in it, so I really don’t know where to start. Thoughts? I’m thinking ignition coil, but I don’t know how to test it.

 

[Joe Reeves]

2005 15hp Johnson.... If it was a coil, dropping out, the drop in rpms wouldn't be a gradual lowering encounter as you described, it would be a sharp drop, sudden, instantaneous.

Possibly you may have picked up a plastic bag and the engine started to overheat, or the water pump is starting to fail?

Could also be a fuel pump acting up or a fuel restriction. Did you by any chance think of pumping the fuel primer bulb, acting as a manual fuel pump?

 

[EastTNHunter]

I did pump the bulb to make sure that it still had prime. I checked the pee hole and water was coming out fine.

 

[EastTNHunter]

I was also wondering about the fuel pump, as you mentioned

 

[oldboat1]

possibly a dirty carb jet.

 

[Joe Reeves]

Water will exit the tell-tale outlet even if the water intake is restricted somewhat or a couple blades break away from the impeller.

It would be a good idea to drop the lower unit to inspect the water pump.

Pumping the fuel primer bulb, acting as a manual pump.... you are bypassing the fuel pumps action, shoving fuel directly thru the pump to the carburetor.

 

[OptsyEagle]

More specifically. Did you think to squeeze the primer bulb "when it was bogging down"? If yes, did it revive the motor or did it continue to bog down?