Hi All,

Just bought a JD STX38 with a 13 hp Kohler Command engine. Engine starts right up.
Problem is at any throttle speed. There is a noise coming from the engine that sounds like a hollow popping noise. It sounds like the noise when there is water in the gas. Engine doesn't hunt and surge, just sounds like a miss in the engine. I took the original carb off and soaked it in carb cleaner. Put it back on and no improvement. Put a good working carb on next and still nothing. It has a new correct plug, new air and fuel filter, new gas.
What am I missing in my hunt to fix this? Fuel flow to carb is good also.

Engine number is CV13S, 21509

Thank you,
Cory

 

That could be a valve not closing or burned. Take a look at valve clearances.

 

I looked on the Kohler website. It said a CV13 had hydraulic valves and didn't require adjustment. Maybe I read it wrong.

 

If everything is working properly, you wouldn't have adjust with the hydraulic setup. But you could have a flat cam lobe = exhaust valve not opening, a burned valve, or a dislodged valve seat. All those things would account for the popping sound you hear.

I believe I would pull the valve cover to see how the valves are moving, then check compression. If low, then pull the head to see where the problem is.

 

Feed it some Marvel oil thru the carb throat while running at fast idle. That will usually cure a sticking valve.
Mike

 

Took the valve cover off and valves look to be operating good. Compression test showed 80 lbs. What should it be to be considered low?

 

On an engine with no compression release, you want no less than 90 lbs, and preferably 120-130. Compression release throws a wrench in the readings though, so your reading can't be trusted. You need a leakdown test. It does sound like a valve problem. Either a sticking valve, cam problem, compression release stuck, or valve seat popping out.

 

Must have been a sticking valve, or something. Dumped some mystery oil in it. Wow, that was alot of smoke. Anyway, I also have a noise whenever I am cranking it over or shutting it down that sounds like a loud click. I took the flywheel cover and I can't see where anything is rubbing or hitting. It doesn't make the noise running. It sounds like it is under the flywheel. Like it is a spring or something. It only clicks once, either when I am starting it or turning it off.

 

That's a normal sound for kohlers. I'm not sure what makes it, I assume the compression release kicking in and out is what makes the noise.