Simplicity Legacy w/25hp Kohler Command running really rich

[macindude]

EDIT: Posted resolution at the end. One cylinder wasn't developing much power due to a bent intake valve pushrod and a bunch of unburned fuel was getting through that side. New cylinder head kit fixed it.

I have a Simplicity Legacy (non-XL) with the Kohler 25hp gas engine. While I was mowing a couple of weeks ago, I fairly suddenly lost power. I found I was able to start the engine, but it didn't have enough power to engage the PTO for the mower. I was able to limp it to my garage.

It appears to be running REALLY rich. Sooty exhaust, carbon fouled plugs, has more power when the air cleaner is off, etc.

I have already taken the carb apart and cleaned the heck out of it, including the main jet that they helpfully hide underneath the fuel shutoff solenoid. I spent way too much money on a carb rebuild kit, could have just bought two cheap Amazon carbs.

At the moment, it really won't run at all unless I remove the air cleaner, and the choke needs to be *off* for it to start. Choke plate in the carb is wide open.

Any ideas as to a good troubleshooting strategy to fix this? I'm not a pro mechanic, I know enough to be dangerous and I like to fix my stuff.

 

[RandyT]

Pull the dipstick and make sure it doesn't smell like gas. The gas fumes in the oil can cause the same effect as the choke being on and will sometimes get better with the air cleaner off. the other thought is the float valve isn't sealing causing overflow of the carb leading to a rich flooding situation.

 

[tomplum]

Other notes: If this has the accelerator pump on the carb, that could create a rich condition if damaged. As well as the fuel pump itself letting fuel into the oil. You seem to be describing a rich condition, but have you confirmed that both cylinders are running? An easy way if you have an infrared thermometer is to compare the exhaust pipe temps.

 

[macindude]

Update:

Upon suggestion from @tomplum, I pulled out my temp gun to verify that both cylinders were running. I was sure they were, since it was just as smooth (or not) as normal, but... They weren't. The right-hand cylinder (the one on the ignition module side, opposite the fuel pump side) exhaust is not even hitting 100ºF in the first minute or so of operation.

I had already replaced and gapped the plug, but I pulled it anyway and it was making what looked to me like a good spark. Dunno what the "proper" way of testing this is, but I just pulled the plug, plugged it back in, started the engine and held it against one of the cylinder head bolts for a ground. It started sparking before I even made contact from the central electrode through the ground and to the bolt on the engine, maybe 3/4" inch away.

So... What else would cause one cylinder to run fine, and the other cylinder to not run at all?

Pull the dipstick and make sure it doesn't smell like gas. The gas fumes in the oil can cause the same effect as the choke being on and will sometimes get better with the air cleaner off. the other thought is the float valve isn't sealing causing overflow of the carb leading to a rich flooding situation.

It actually does kinda smell like gas inside the filler. I'm guessing this is just because of how much I've been running it with one cylinder dead?

Other notes: If this has the accelerator pump on the carb, that could create a rich condition if damaged. As well as the fuel pump itself letting fuel into the oil. You seem to be describing a rich condition, but have you confirmed that both cylinders are running? An easy way if you have an infrared thermometer is to compare the exhaust pipe temps.

It does have the accelerator pump, but when I cleaned up the carb I did take that apart and inspect it, and it's in surprisingly good shape. But you were right, only one cylinder is running as described above. What could be causing that?

 

[RandyT]

What model of Kohler engine is this. Different issues can arise depending on model.

 

[5030]

I know in my case. it was mouse chewed wiring that went from the magneto to the coil packs. Just enough insulation chewed off to render the one cylinder inoperative with the air shield (top of the motor installed).

 

[Topzide]

Check the compression on the cylinder not coming up to temp. A build up of debris around the cylinder head can cause head gasket leak. Having spark is only part of the equation. You need spark, fuel and compression to run. Have also seen the decompression Valves stick open.

 

[tomplum]

Checking the compression is a good thing. Commands are mechanically pretty stout, but a migrating exhaust valve seat happens in a blue moon. Usually a non firing cylinder on a Command goes back to an ignition issue. It sounds like you have SAM ignition. Like Randy said, the model and spec is real helpful in situations like these.

When you say soot, I'm thinking loose black practically powdery stuff as opposed to hard carbon and plug fowling type of thing? Correct?

So an engine that decidedly runs on 1 cylinder leaves unspent fuel in a cylinder more so with compression, but it would figure that it would run rich anyways as twins are like that. That would be soot.

I hated buying accelerator pump kits, so cheers to a good diaphragm. The carb kits as you eluded to are crazy expensive, let alone to price a carb complete.

Grab a compression gauge off the Napa loaner counter and do a comparison of the two cylinders or a leak down test if you can swing it.

 

[macindude]

What model of Kohler engine is this. Different issues can arise depending on model.

CH25S - 68583.

Check the compression on the cylinder not coming up to temp. A build up of debris around the cylinder head can cause head gasket leak. Having spark is only part of the equation. You need spark, fuel and compression to run. Have also seen the decompression Valves stick open.

I don't have a compression tester... At least, not yet.

But, just to ensure that there isn't anything wrong with the plug, I'm going to swap the spark plugs tomorrow and see whether the problem follows it or not.

The buildup of debris causing a leak is a definite possibility too. I did do a lot of cleanup when I had the engine out briefly, but I didn't pull the covers over the heads so there's still some in there.

If there's a valve sticking - What's the solution for that? Sounds like major surgery at that point.

 

[macindude]

Checking the compression is a good thing. Commands are mechanically pretty stout, but a migrating exhaust valve seat happens in a blue moon. Usually a non firing cylinder on a Command goes back to an ignition issue. It sounds like you have SAM ignition. Like Randy said, the model and spec is real helpful in situations like these.

When you say soot, I'm thinking loose black practically powdery stuff as opposed to hard carbon and plug fowling type of thing? Correct?

So an engine that decidedly runs on 1 cylinder leaves unspent fuel in a cylinder more so with compression, but it would figure that it would run rich anyways as twins are like that. That would be soot.

I hated buying accelerator pump kits, so cheers to a good diaphragm. The carb kits as you eluded to are crazy expensive, let alone to price a carb complete.

Grab a compression gauge off the Napa loaner counter and do a comparison of the two cylinders or a leak down test if you can swing it.

Here's the data plate:



Didn't know there was such a thing as loaner tools at Napa!