Kohler/Yanmar 12.5 Issues - Printable Version

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+--- Thread: Kohler/Yanmar 12.5 Issues (/showthread.php?tid=8974)

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Kohler/Yanmar 12.5 Issues - TeamPunisher - 05-26-2026

Lost a generator water pump on our first long trip, was able to get it fixed a day later, then genset ran fine for a couple days.
 Then early one morning it made some noises and shut down. It will re start, runs up to rpm, then slows to an idle then shuts down again.. 
Engine sounds fine, there was a round piece of plastic in generator compartment, and black dust around head unit.. 
Can I be lucky and just need brushes or something? I'm a mechanic, but not familiar with gensets.
I tried calling martin but no response yet.

What are the experts thoughts on keeping this old unit going vs. updating to something newer?

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RE: Kohler/Yanmar 12.5 Issues - Richard - 05-26-2026

First order is change fuel filters.

How long does it run before shutting off? Is the shutdown quick or does the engine stumble? What does the fuel shut off do in conjunction with the shutdown?

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RE: Kohler/Yanmar 12.5 Issues - TeamPunisher - 05-26-2026

(05-26-2026, 03:09 PM)Richard Wrote:  First order is change fuel filters.

How long does it run before shutting off? Is the shutdown quick or does the engine stumble?  What does the fuel shut off do in conjunction with the shutdown?

I don't believe it is an engine issue, it starts and runs up to governor, then within a couple seconds it slows to an idle speed for about 5 seconds, then shuts down. Engine sounds perfect the whole time. Zero AC voltage output though.

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RE: Kohler/Yanmar 12.5 Issues - folivier - 05-27-2026

Just an FYI that engine is a tractor engine if I remember correctly. Might make it a bit easier to source parts.

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RE: Kohler/Yanmar 12.5 Issues - bestgenman - 05-27-2026

If the engine accelerates to rated speed and slows down,  there are a couple of things you need to know, is the fuel solenoid pulled in? (Visual or voltage check),  does the engine exhibit black smoke? (Indicates high load).

Typically, the controls don’t allow the engine ignition system (the 12v that keeps the solenoid in, the gauges alive, and lift pump running) to stay alive without ac voltage.  So that might be the case here, no ac volts and the ignition system goes down but the solenoid linkage is binding keeping the engine running at low speed.

No mention of hours but Kohler brush style ends usually run 7000 hours or more before needing brushes.  If you can get to the brush holders, look at brush length.  If it’s good or decent, the regulator might be faulty.

Of course the fuel system could also be the reason the engine speed drops.  Lots to check but I think you have two issues here.

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