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I have a Cub Cadet model 1515 lawn tractor my neighbor gave me that he got tired of messing with after it wouldn't start anymore. When he gave it to me all it needed was a new starter and battery and it fired right up! This tractor has a 15hp Kohler Command CV436 single piston engine. Once I knew it would run I changed the oil and filter, spark plug (gapped to spec), fuel filter, air filter.

After I've been using it to mow my yard, I've been noticing after about 15-20mins of runtime the engine would bog down under load where it almost stalls out, but never actually dies (yet...). It only does this when the PTO is engaged. When it starts to bog down I do 1 of 2 things:

A. let off the throttle and let it catch itself
B. disengage the PTO and let it catch itself

I cut the grass at least once a week so its not like the grass is getting too tall for the mower.

I was leaning towards a fueling problem. So I pulled the carburetor apart and cleaned it. It didn't look dirty at all when I cleaned it. That did not fix the issue. I adjusted the idle speed knob to give it a little more fueling but the only impact that had was adjusting the low idle speed. The other adjustment on the carb had a lock cap on it from the factory so I left it a lone and I don't think its truly a carb issue after seeing a nice full bowl of fuel and how clean it was. I also noticed the fuel line was dry rotted so I pulled the gas tank out and replaced the line. That had no impact either. I have not touched the fuel pump or ignition coil yet. But I doubt its a fuel pump because the carb seems to be getting fuel. My neighbor said he has replaced the ignition coil in the last year or two. I haven't ruled these out yet, but seems unlikely to me.

Then I noticed it seems like the engine is running hot. I say this because if I pull off the 2 side panels on each side of the engine it runs fine under load. So it seems like its not getting enough air flow. I have check the intake screen and shroud and all is clear. I even hosed down the engine to clean it up and make sure there is no debris anywhere. I have made sure the oil level is correct and its at the full mark. I put 2 quarts of 10W-30 in when I changed it.

The only other thought I have is that the muffler seems to have a leak and maybe its letting too much hot air into the engine compartment heating the engine even more. Even if it wasn't leaking its kindof a bad design in my opinion because the outlet faces the front of the tractor and there are air inlets up front under the headlights so its basically just blowing hot air in its own path.

When searching online it seems in general all various types of Kohler engines run into this problem (mostly twin cylinder) and I never see a solution. I'm trying to logically trace the problem without throwing all the parts at it. Does anybody know common problems with this engine related from this symptom and what to try next?

I can post some pics later if that helps so you can see the condition its in.

What type of oil are you running in it, and under what sort of temps? Most small engines are hard working, and require a straight weight oil. 30w if you're in the mid 20's C, which would be mid 70's F, and up from there if hotter. An average HD motorcycle will run a 20w50 in the summer time, just to keep it cool. Oil is as important as anything, and your average car oil isn't going to do the job.

I put conventional 10W-30 in it. Same as what the operating manual said to use. Its been operating like this at 65-90F outside

Check the alternator output at the battery by reading battery voltage:-
engine off
Engine on PTO off
Engine on PTO on

Let us know the numbers to one decimal place

When you said you cleaned the engine, did you remove the blower housing and clean all of the cooling fins ?

If you have a compressor, stick an air duster under the flywheel and blow the dust out.

While you are there, pull the bolt out of the flywheel and check that the slot of the key is a perfect square.

Other than that, a weak throttle spring will allow the governor to hold the throttle plate a bit too far closed when the engine is under load

The service manual for your engine is available from Kohler ( sign in as a guest ) and some other places if you have problems getting it there.

You should pull the shroud and make sure all the cooling fins are clear of debris. Air is the only thing that cools these small engines.

Here is a pic from the top. I took it so I could remember what engine model i have. Ill get some more pics of the sides. I have not taken the cover off and cleaned the fins. Ill try that too. I just hosed the engine down to get all the debris off and spray water in the bottom between the oil sump and frame. Ill also measure and post alternator voltages later. Thanks!

bertsmobile1 said:

Check the alternator output at the battery by reading battery voltage:-
engine off
Engine on PTO off
Engine on PTO on

Let us know the numbers to one decimal place

When you said you cleaned the engine, did you remove the blower housing and clean all of the cooling fins ?

If you have a compressor, stick an air duster under the flywheel and blow the dust out.

While you are there, pull the bolt out of the flywheel and check that the slot of the key is a perfect square.

Other than that, a weak throttle spring will allow the governor to hold the throttle plate a bit too far closed when the engine is under load

The service manual for your engine is available from Kohler ( sign in as a guest ) and some other places if you have problems getting it there.

Click to expand...

Hey Bertsmobile 1

I finally got around to getting the battery voltage.

Engine off = 12.78V
Engine on PTO off = 13.96V
Engine on PTO on = 14.28V

Since you guys said to check the fins in more detail, I pulled the cover and didn't really see much of anything in the fins. The cylinder head fins had some gunk but not sure if that is considered bad enough. Check out the pics and let me know what you think. Thanks!

OK,
First thing is have you located & checked or bypassed the 7.5A fuse shown on the purple wire ?
The switch is shown in the OFF position and in that state the top contacts allow power to the starter solenoid
The two lower pairs of contacts are open & do nothing.
In the ON position the lower 2 pairs are closed.

The bottom pair turn the clutch on & off but the middle pair activate a ground circuit to the M contact ( Magneto ) on the key switch.
If the seat switch contacts are closed ( yer bum ain't on it ) then the magneto is grounded and the engine turns off.

You can test the PTO switch by sitting on the seat and working the PTO switch.
If the fuse in the power supply is good you will hear the PTO go Klunk.
There are 4 circuits that ground the magneto
1) key switch M + G
2) lap bars & parking brake
3) parking brake + seat switch
4) Seat switch + PTO

These circuits all work in parallel so any one of them closes & the engine stops

Hey Bertmobile1

Was my alternator voltages good?

Also can you explain to me what Im looking for in the circuitry that leads to the engine bogging down under load? Just trying to understand better what your having me look for? Thanks in advance for helping

Sorry I have cross posted .
With a bit of luck the post with the confusing stuff will be gone.
yes those numbers were good so you can cross off the alternator from the list of culprits.

In a situation like yours I generally blame debris in the tank causing a plug which restricts the fuel flow.
However this generally causes surging on governed engines and you just complained of a loss of power.

In that case I would lean towards flooding

Next time you mow, when it plays up, set the hand brake , jump off and manually push the governor arm to open the throttle
IF the engine picks up & runs well then adjust the governor according to the instruction in the Kohler manual.

Not sure if that engine has hydraulic lifters or solid adjustable lifters but in any case it won't hurt to whip off the rocker cover & check the valve lash.
Too big a clearance leaves the exhaust in the cylinder for a poofteenth of a second longer on each power stroke which causes the engine to run that little bit hotter.
It also opens the inlet a poofteenth latter so you don't get as much fuel in each charge.

When the engine is under load, the governor should allow the throttle to open right up and full throttle will make the situation worse.

Also whip the guard & retaining bolt off the flywheel and do a quick visual of the timing key.
The 2 halves should come together to make a perfect square, even if they are slightly off square that puts the timing off and that causes loss of power & overheating as well.

Thanks Bertsmobile! Lol no problem on the mix up. I checked out the flywheel key and it doesnt looked sheared. I think im just going to blast off those fins with cleaner so they look new and see what it does before I start tearing the engine completely apart.

I pulled the tank out before and put a new fuel line in so I think that is good. But I didnt pay that close attention to the inside. Fuel definitely comes out of it when I changed the line haha. Ill play around with the governor some like you suggested.

Quick Update. I took all the engine covers off and cleaned the cooling fins really well with brake clean. Also found a metal adapter fell off inside the muffler. I reattach that with self tapping screws. Some exhaust air still comes out but not as bad. I think that never had a comeplete seal from new from the way it was designed. Mowed the yard today and had no loss of power issues. It was 82F out when I mowed. I think its fixed! Thanks all for the help!