Baffled by Mariner 25hp

[Rock Hall]

I have a mid 80s Mariner 25 hp motor. I've been trying to get this motor right for almost 2 years. When cold, starts fairly easy. 2nd or 3rd pull. After warm up, runs great. Has always been a little rough at low RPMs, but really runs good otherwise. After about 15 min of running, will just shut off. At this point, it will usually start right back up 1st pull and run for another 10 min or so, then shut off. Now it will need to sit for 5 min, then will start right back up 1st pull. Each time, it runs for a shorter amount of time and needs to sit longer before starting. So, I've concluded that it is a heat issue. A few years ago, this happened and then failed to start at all, even when cold. So I started replacing parts. Started with switchbox, no change. Then trigger coil and finally the stator fixed the problem. I honestly cant remember if it ran 100% after that repair. I think I still had the shut off problem, but it would go for a few hours.
Here is a list of what I have done to this motor in the past 2 seasons:
1. New Stator
2. New Ignition Coils (both)
3. New Trigger coil.
4. Partial rebuild on Carb to include Fuel pump.
5. drained and cleaned fuel tank. New Gas
6. New Plugs
7. New Plug Wires
8. New Switchbox
9. Disconnected Kill switches


I think that covers everything. I have a new priming ball that is going on this weekend. I am also going to put the old switchbox back on. I'm thinking I might have a bad stator again. It's an expensive part I've been putting off buying another. I do know that the timing is probably not correct. When it was running I adjusted the timing all over the place to try to get it to run better.

So if anyone has any suggestions, please let me know. I would take it to the shop, but I think they would have a hard time duplicating the problem and I'd end up the the motor the same and a big bill for their time. I'm leaning toward the possibility that one of the new parts I bought has failed. I do have a spare switchbox, but thats it for spare parts.

Thanks
Mark

 

[Vlad D Impeller]

Re: Baffled by Mariner 25hp

Could it be that you may be experiencing fuel starvation, due to lack of the fuel tank ventilation?

 

[Rock Hall]

Re: Baffled by Mariner 25hp

That was a thought. The vent is completely open on tank. Replacing the ball this weekend. There have been times when I forgot to open the vent and it seemed to be a more gradual shut-down when that was the case. This is like hitting the kill-switch (which I have tried unplugging)

Also I replaced the entire water pump. Forgot to mention that in the previous post.

I'm going to put the old switchbox on this weekend also. The bad thing is, every test results in me having to paddle back to the ramp while hoping for a tow.

 

[Rock Hall]

Re: Baffled by Mariner 25hp Shut off

Re: Baffled by Mariner 25hp Shut off

Does anyone know if this motor has some kind of safety shut down for when it overheats?