1998 Merc 15 HP 4 stroke no spark

[Swedefj40]

I use my 1998 15 HP 4 stroke Merc (OG674558) mainly for trolling (off idle to maybe 1500 RPM) and my last trip out, it ran fine for about 10 - 12 hours non stop. No issue. Next day out it ran great for about 30 minutes then seemed to struggle slightly for about 10 seconds then it shut off. I restarted it and it ran for 20 minutes or so then same thing. It did the same thing x2 more and finally I gave up and trolled with the main engine. In the mean time I pulled the carb off and tried to clean out the idle jets and after that it ran for almost an hour then died again. Next day it wouldn't stay running at all. Yesterday I tried it again in the driveway and it ran for 5 minutes then died. So all along I'm thinking fuel issues as I've had issues with the carbs jets clogging up but it seems good. Fuel filter was a bit restricted so I changed that out. No difference. Fuel pump is working as well.

So now I'm thinking electrical. I pulled the plugs and sure enough, no spark. I checked the kill switch at the motor and Tiller and both are functioning (N/C "off" and N/O to "run"). Oil press switch is in the N/C state when not running. Coil was measured out to 0.4 Ohms.

What's next? CDI and magneto?

 

[Swedefj40]

Anyone have a wiring diagram for this motor?

 

[Swedefj40]

Rectifier checked out okay

 

[Thirsty Endgrain]

I can't help with your situation, but I can recommend getting your hands on a factory service manual. I just got mine in the mail from eBay today, and within 10 mins of perusing it I've been able to answer about 27 questions I've had in my head (and asking on the forums) about my engine. Every wiring diagram you could want.

If however, your engine will run periodically like that I'd maybe be looking for a wiring fault, maybe from the kill switch.

 

[Swedefj40]

I'd love to have an actual service manual but I'm in a bit of a time crunch (as always). I think I've narrowed it down to the Pulser or CDI... just trying to dig up the proper way to test them.

 

[Thirsty Endgrain]

I'd love to have an actual service manual but I'm in a bit of a time crunch (as always). I think I've narrowed it down to the Pulser or CDI... just trying to dig up the proper way to test them.

I understand the crunch (always). But asking for help on the forums can at times be slow, which is just how it is, and I'm always thankful for when folks who know are generous with their time and information.

But the FSM has all steps and troubleshooting right there in front of you, including testing methods that are very clear. Maybe get yourself one on the way for next time, or possibly even this time...

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