25hp Kohler Command shutting off under load

[d6s]

First post here looking for some help. This thing has been driving me up a wall.

Put a mikuni carb on my 25hp Kohler Command that powers my boat.

First trial run it would idle perfect but under 50% throttle and 100% throttle it would cut off after about 20 seconds.

Last time I had it out…. About a week ago (only thing I did was unplug the oil pressure sensor) it ran like a dream and I figured for some reason it was fixed.

Took it out today and it’s the same thing, 50% throttle and 100% throttle it cuts off.

It smells like it’s running a little rich but it dies like it’s running out of fuel.

I have a 12V HEP-02A electric pump rated at 2.5-4psi going into a pressure regulator set at 1.5psi with a return line between the pressure regulator and the carb for unused fuel to return to the fuel tank.

I was going to replace the flywheel and lifters since others before had suggested that since it runs right around 4000 rpm wide open but I’m not sure if that would cause it to cut off at ~2800 rpm like it is at 50% throttle.

I have some videos of it running and can take some pictures if the fuel pump/pressure regulator setup as well.

Thanks y’all.

 

[userfriendly]

It sounds like the carburetor is running out of fuel possibly because the fuel pressure is too low going into it.
Try raising the fuel pressure to 4 psi and see what happens.

A larger needle and seat may also fix the problem without raising the fuel pressure.

 

[d6s]

It sounds like the carburetor is running out of fuel possibly because the fuel pressure is too low going into it.
Try raising the fuel pressure to 4 psi and see what happens.

A larger needle and seat may also fix the problem without raising the fuel pressure.

The reason I put the regulator on to begin with was because the pump was just pushing fuel out of the overflow. I’ll try setting the regulator to 4psi when I run it tomorrow.

 

[eljefino]

What was it that caused you to change carbs?

I wonder if you're loosing compression as it heats up.

 

[oilcandave]

What eljefino said...check valve lash. When those motors are used in a boat they run hot.

 

[Slick3914]

The fuel tank vent could be the culprit as well.

 

[k1xv]

Do these things have a fuel filter? Clogged?

 

[jeepman3071]

What eljefino said...check valve lash. When those motors are used in a boat they run hot.

Kohler Command 25hp should have hydraulic lifters.

 

[mk378]

Take the top cover off and look for mouse nest etc blocking the cooling system.
You could disconnect the ignition kill wire at the engine to rule out electrical problems in the boat.

 

[Slick3914]

Take the top cover off and look for mouse nest etc blocking the cooling system.
You could disconnect the ignition kill wire at the engine to rule out electrical problems in the boat.

That’s a really good suggestion as well.

 

[JimPghPA]

What type of ignition system does it have?