Kohler

[shrodney]

New issue: I have been asked to fix a mower with a 12.5 hp Kohler, single-cylinder, OHV, air-cooled, vertical shaft engine. It mows for about 20 minutes and then the motor wants to spit and sputter and die. If I choke it, I can get about 5 minutes more out of it before it dies for good. Then it has to sit for about 2-3 hours before it will start and run normally again. Rebuilt carb and replaced mounting gaskets thinking that it was sucking air. No joy. Fuel is clean, fuel filter good, fuel cap vent is good, good spark, still has about 160 lbs of compression hot, new air filter. Stator is charging the battery. No oil pressure or thermal shutdown features on this motor. Valves? Coil (electronic) overheating and not in time? The reason I did the carburetor was that I had the same thing recently on a weedeater and that fixed it - one of the carburetor mounting gaskets was worn and the heat exploited it (I guess). ANY advice would be greatly appreciated! Thanks!

 

[Tazza]

The only thing i can add to what you have already done is to ensure the fuel hose is far enough away from the engine. Could it be vapour lock from the fuel getting hot and evaoprating causing the fuel to not reach the carb in a liquid state? I know this has been an issue for me before, but not sure it it would apply to you or not.
As you mention the choke keept it running a little longer still makes me lean towards fuel. Can yourty elevating the fuel tank a little more? see if its not getting quite enough fuel pressure to the carb when its warm.
There are so many “maybe” things.

 

[shrodney]

The only thing i can add to what you have already done is to ensure the fuel hose is far enough away from the engine. Could it be vapour lock from the fuel getting hot and evaoprating causing the fuel to not reach the carb in a liquid state? I know this has been an issue for me before, but not sure it it would apply to you or not.
As you mention the choke keept it running a little longer still makes me lean towards fuel. Can yourty elevating the fuel tank a little more? see if its not getting quite enough fuel pressure to the carb when its warm.
There are so many “maybe” things.

Tazza, thanks for the advice. I did shorten the fuel line, but that didn't help. But, it would run fine if I parked it sideways on my hill with the tank uphill from the pump. Turns out that what it was was this: the carb WAS sucking air via the fuel pump (mechanical diaphragm type) because the outlet from the pump to the carb had a blown seal, so when it got hot enough to cause enough distortion of the seal, the vacuum from the engine via the carb was sucking air from the fuel pump. That's why I could choke it and get a few more minutes out of it. Replaced the seal and ran it for 2 hours until I saw that I couldn't get my lawn any shorter. I ran it hard, too, and not even one burp. Pretty interesting find. I never considered a carb sucking via a fuel pump. That's one to remember! Thanks again for the advice!

 

[Tazza]

Tazza, thanks for the advice. I did shorten the fuel line, but that didn't help. But, it would run fine if I parked it sideways on my hill with the tank uphill from the pump. Turns out that what it was was this: the carb WAS sucking air via the fuel pump (mechanical diaphragm type) because the outlet from the pump to the carb had a blown seal, so when it got hot enough to cause enough distortion of the seal, the vacuum from the engine via the carb was sucking air from the fuel pump. That's why I could choke it and get a few more minutes out of it. Replaced the seal and ran it for 2 hours until I saw that I couldn't get my lawn any shorter. I ran it hard, too, and not even one burp. Pretty interesting find. I never considered a carb sucking via a fuel pump. That's one to remember! Thanks again for the advice!

So simple, yet so frustrating trying to find it.
Always good to hear a good outcome.