Help Diagnosing Issue

[MrLarkins]

First time poster here, thanks in advance.

I'm running a Husqvarna RZ5426 with a Kohler SV735 (Courage 26hp 725cc). I purchased it new years ago and have maintained it well. This season something has changed. Let me describe the symptoms and tell you what I've looked at already.

Symptoms:

1. Runs a slight bit rougher than normally. By this, I mean that the engine shakes more than years past, but it isn't much.
2. Starts fine and runs for a good 15 mins; Then the engine will wain when under a strain, to the point where it dies. This can be mitigated somewhat by disengaging the blades and releasing the handles so that it idles in neutral.
3. If the engines does shut off, it can easily be restarted, but runs best if let set to cool down.

What I've looked into:

1. I've checked the oil level; it is full but not overfull. Oil is clean from a recent change.
2. There is no smoke in the oil fill pipe as would be the case if a head gasket was leaky.
3. The carb was taken off, apart and cleaned. No trash was in it.
4. Gas is fresh, and fuel filter was replaced last year. Fuel pump was tested and is pumping as it should.
5. Air filter is new for the season and not clogged.
6. Battery is 1 year old and holds at 12.8v.
7. Spark plugs have spark. I did disconnect each spark plug momentarily to see if each cylinder was firing. I did this quickly so the engine wouldn't run too long...just a couple of seconds. Each cylinder ran fine.
8. I cleaned the debris was the engine block fins, thinking it was a cooling issue. one side seems clogged with grass, but there was no oil leaks anywhere on the block, and I looked hard after taking covers off.

The only defect I did find was a crack in the muffler.

Okay, there it is. Any suggestions of what I should look into next?

 

[Rivets]

First thing I would check are the valve clearance. This manual may help you out. https://resources.kohler.com/power/...1.1295208345.1687544055-1693047200.1687544055

 

[MrLarkins]

Thanks for the suggestion. I took off the valve covers and a pool of oil spilled everywhere. I was ready for a little bit, but this seemed excessive. I checked the clearance, and all four were spot on. I resealed with Permatex Ultra Red. In an hour, I'll torque it down. Will run again tomorrow.

 

[Rivets]

Hate to say this but did you removed the shroud and check the crankcase bolts to see if any were loose? The Courage engine had a big problem with these bolts coming loose. If they are not tight as the engine heats up and your timing might be changing causing a loss of power. I’ve never heard of loose bolts causing this problem, but this engine has had unusual problems in the past. Also it might be worthwhile to purchase an inline spark tester and insert it into one of the plug lines, looking to see if the spark changes when the problem occurs. Will need to do both cylinders separately, unless you get to testers. If the spark changes you may have a coil which is starting to breakdown. We need to figure out whether it is a spark or fuel issue. If spark stays strong and consistent, we go to a fuel problem.

 

[Tiger Small Engine]

Hate to say this but did you removed the shroud and check the crankcase bolts to see if any were loose? The Courage engine had a big problem with these bolts coming loose. If they are not tight as the engine heats up and your timing might be changing causing a loss of power. I’ve never heard of loose bolts causing this problem, but this engine has had unusual problems in the past. Also it might be worthwhile to purchase an inline spark tester and insert it into one of the plug lines, looking to see if the spark changes when the problem occurs. Will need to do both cylinders separately, unless you get to testers. If the spark changes you may have a coil which is starting to breakdown. We need to figure out whether it is a spark or fuel issue. If spark stays strong and consistent, we go to a fuel problem.

Timing is controlled by the flywheel key. The shaking engine is probably loose or lost engine mounting bolts. The Kohler Courage is a dog and has several problems. Read up on it online and definitely check the top cover engine bolts for tightness under engine shroud.

 

[Rivets]

Valve timing is controlled by camshaft, which could wobble if the cover comes loose. Slight change in valve timing can cause loss of power.

 

[Tiger Small Engine]

Valve timing is controlled by camshaft, which could wobble if the cover comes loose. Slight change in valve timing can cause loss of power.

I realize that valves are controlled by camshaft. Thought you meant ignition timing.

 

[bertsmobile1]

This will also happen if one cylinder is not firing
IT will run sort of OK for a while although being a bit under power then will overheat .
From dead cold start the engine and lightly touch both exhaust pipes.
If one is substantially hotter than the other then that side is not working properly .
Let us know what you find

 

[StarTech]

Rivets this is not the bucket engine. It just a Briggs crankcase design wise. It was the Kohler single cylinder bucket engine that had the closure plate bolt coming loose over time. Some of those actually broke the cylinder off the crankcase until Kohler re-enforced the area.

 

[VegetiveSteam]

Hate to say this but did you removed the shroud and check the crankcase bolts to see if any were loose? The Courage engine had a big problem with these bolts coming loose. If they are not tight as the engine heats up and your timing might be changing causing a loss of power. I’ve never heard of loose bolts causing this problem, but this engine has had unusual problems in the past. Also it might be worthwhile to purchase an inline spark tester and insert it into one of the plug lines, looking to see if the spark changes when the problem occurs. Will need to do both cylinders separately, unless you get to testers. If the spark changes you may have a coil which is starting to breakdown. We need to figure out whether it is a spark or fuel issue. If spark stays strong and consistent, we go to a fuel problem.

Just to clarify if I may, the issue with the loose bolts was on only Courage single cylinder engines where there was no removable oil pan and you got to the inside of the engine by removing the top closure cover of the engine. Those did indeed have some loose fastener issues.
Ooops... Just noticed Star already addressed this.