Lawnmower engine trouble

Any small engine guru’s on here?

I have a Dixon 2300 zero turn with a Kohler Command Pro 23. The engine misses badly especially at low RPM. It seems to smooth some at higher RPM and is still generating enough power to mow.

I just got this mower from my dad, and he put new plugs, fuel filter and air filter on before giving it to me. The weird part is, when running, if I remove one of the spark plug wires, the engine runs really smooth. This only works with one plug wire. Removing the other one has no effect. I was trying to check which cylinder was having issues by removing the wires, but running smooth with one missing has me baffled. Has anyone experienced this before. What does it indicate?

Chad

make sure the flywheel is tight,and be sure the blades are tight.

Is it missing or starved of gas at low rpm? I’d check the gap on the plugs to make sure he got the correct ones first. 10 second check.

Have you replaced the spark plugs?

Plug wires going to the correct cylinder?

Check the coils?

Might be worth getting a compression and leakdown test to be sure you don’t have a stuck valve or something.

It’s giving off a lot of fumes through the exhaust when running, so there is gas getting there that is not getting burned.

He was having the missing issue before the new plugs. He was hoping that and the filters would fix it. I will still check the gap.

Pete, spark plugs are new, wires are correct. It has an ignition module, which I am not sure how to check.

If one of the cylinders did not have compression, wouldn’t the mower die when the plug wire was removed from the other cylinder?

That’s why this is such a mystery to me. Removing the one plug wire seemed to fix the issue, which makes no sense to me.

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It’s giving off a lot of fumes through the exhaust when running, so there is gas getting there that is not getting burned.

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You’ve probably got a dead cylinder. That raw fuel symptom is a pretty strong indicator and some engines will run ok with a dead cylinder, but it’s exactly as you described, only in the upper RPM range.

I’d use a spark checker to see if there’s spark in the suspect cylinder. But from there it gets a little tricky, as it could be the coil, the CD module, or other. Trying to chase the problem by parts swapping could get expensive and time consuming, so this is the point where it might be worth taking it in to someone who can diagnose and one-shot fix it.

Grouse

Thanks for the feedback Grouse. If it has a dead cylinder, wouldn’t the engine quit when I remove the plug wire to the good cylinder?

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Thanks for the feedback Grouse. If it has a dead cylinder, wouldn’t the engine quit when I remove the plug wire to the good cylinder?

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Maybe. The cylinder may not be entirely dead. Or you could have a CDI or coil issue such that enough spark isn’t being generated when both cylinders are runnning.

We’re sure the plug wires aren’t reversed, right?

A carb issue isn’t outside of the realm of possibility, a valve issue is possible as well. Also, it could be a combination of things, for example a weak spark could have been causing incomplete combustion and carbon buildup, which could cause the valves to stick…

Not an easy one to diagnose without being able to test a coil, CDI, and possibly leakdown test for valve and cylinder issues.

Grouse

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Pete, spark plugs are new, wires are correct. It has an ignition module, which I am not sure how to check.

If one of the cylinders did not have compression, wouldn’t the mower die when the plug wire was removed from the other cylinder?

That’s why this is such a mystery to me. Removing the one plug wire seemed to fix the issue, which makes no sense to me.

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If the exaust valve is leaking or something, the engine would still run, just not well.

A compression test is where I would start.

Pull the plugs after running it for a short time and if one cylinder is wet it is a spark issue. I have had similar issues with Honda motors. The Honda motor has a electronic box for each cylinder. I found one electronic box bad in each case. The one that had a wet cylinder will be the bad one.

Do a compression check on both cylinders. They should be no more than 10% difference between the two. And a typical compression reading should be at a minimum of 110 psi and maybe a high as 125 psi .

Thanks for the ideas guys. Looks like I have some more work to do when I get time.

Take both plugs wires off and take the sparkplugs out and put the wires back on and ground them to somewhere on the engine. Have someone turn the engine over and see if there’s a nice and blue spark on both plugs. It has to be blue and not a shade of red or any other color. If the sparks blue I’d still check out the ignition module or coils if it has coils. Sometimes wires rub against the underside of the flywheel and short out intermitently. Ignition modules I know nothing about but coils and condensers I do. Take a compression test too because that will tell you if one of the valves isn’t sealing right on its seat when its closed. It should be within 10%. Another thing is just because their new plugs doesn’t mean their firing right. If you have an old plug clean, gap and retry that one and change plugs around. If its only on the one cylinder its either ignition or the valve isn’t closing or maybe even partially opening if it has a bent valve stem. If you get into the motor a ways it doesn’t hurt to take the carb apart and clean each air and gas passage and each piece with carburetor cleaner, if you can. It might be a whole lot easier to just take it in and have someone check it out for $50 bucks or maybe even cheaper. It could be that side of the ignition module that goes to that cylinder is weak. Check the spark first, then go from there. I do my own tune ups on my boat motors, lawn mowers and cars and it does sound like a spark issue because there’s an intake manifold that feeds both cylinders, from one carburetor, if one side runs good the other should too. I doubt its a warped valve stem but the valve may not be seating right. I just got done working on two kohler 14 horse engines and lapped in the valves in them on both of my 1450’s and the compression went from 60 to 120 pounds. It could be a lifter needs adjusting which isn’t that hard either. If you have any other questions pm me and I’ll try to help. Good luck.

Thanks for the pointers Dan, and the offer to help. It will probably be a few days before I get a chance to look into it.

Thanks Hof, Just message me if you need help. Stay away from Champion plugs as they fowl to easy, go with NGK’s or Bosch platinum plugs. The better motorcycle shops around here use both but mainly Bosh platinum plugs. I run NGK’s in all my motors including my boat motors and they never fail.

Just though of another thing. Go out at night where there’s no light and get it started and look at the engine to see if the plug wires are arcing out, you’ll be able to see it if they are, but look closely without a flashlight, sometimes its a dim short and can barely be seen but enough to make the spark weak.