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CC XT1 LT42 with Kohler 5400 series engine 18hp and has 39.9 hours.

The engine starts and runs great even with the throttle at the lowest (turtle) position. When the throttle is moved to the fastest position the engine runs smooth and steady. But, when the blades are engaged the engine begins to buck and will occasionally backfire. Disengage the blades and the engine runs great at any throttle position.

I have cut two 1/4 acre lawns with the mower. First lawn everything worked fine. Second lawn with a little higher grass and if a clump of thick grass was cut, the engine would begin the run rough. If the blades were disengaged and the mower just sat for a 15 to 20 seconds, the engine would begin to run smooth again and would run and cut fine. Encounter another thick clump of grass and same stalling would happen. Now it is virtually impossible to cut grass, 3 lawn, without potentially damaging the engine.

I just acquired the mower so I am not sure of past maintenance practices, however, the oil was at the proper level and looked new when I acquired the mower. I do not know but doubt that the gas was drained over winter. The mower was built in 2018.

I checked the spark plug and it was dry with no buildup of deposits. The air filter is relatively clean - I don't think the filter is the problem.

Any opinions or suggestions would be appreciated.

Thanks

Used mower alert. Check everything over.

IMO, under load means the carb main jet is partially clogged or some fuel delivery issue. Dirty tank, carb needle and seat or float adjustment.

Others like tire pressure, deck too low for the grass height and pulley bearings going out slash locking up. Sharp blades?

slomo

I agree with the lack of fuel, next time it acts up loosen the gas cap ,maybe the cap vent is restricted, then change the fuel filter or at least remove and back blow through it into your hand to se what's in it if anything. It does sound like the taller grass is pulling the governor opened and there is not enough full in the bowl to feed it.

Might be a fuel cut off valve failing if one is installed partially blocking the fuel flow. Lame fuel pump if it has one. Several things could cause this under load issue.

slomo

Thanks slomo and Rocky J for your feedback. Can't judge a book by it's cover. I looked at the air filter and it looked relatively clean, nothing to get concerned about. Thinking what is the easiest thing I can do first to start the elimination process - remove the air filter. I did that and the engine started and ran really smooth and strong even when the blades were engaged. The problem appears to be totally the air filter.

I took the 'clean' outer foam sleeve off the tubular air filter and the filter was horribly dirty with dusty dry dirt particles.

I ordered a new filter and spark plug from Cub Cadet. They are really proud of their air filters, but homedepot is even more proud - $41.00.

Anyway, thanks again but I think the air filter is the culprit. If not, I'll update this.

Wonder what your spark plug looks like? Bet she is clean and clear running that lean. Just goes to show how rich these engines are.

On a good running engine, the plug will need cleaned yearly from carbon. Every one I've seen tend to run on the rich side. Compare it to your plugs in your car or truck. Those look like you just installed them after 75,000 miles. Good ol' EFI there.

slomo

slomo said:

Wonder what your spark plug looks like? Bet she is clean and clear running that lean. Just goes to show how rich these engines are.

On a good running engine, the plug will need cleaned yearly from carbon. Every one I've seen tend to run on the rich side. Compare it to your plugs in your car or truck. Those look like you just installed them after 75,000 miles. Good ol' EFI there.

slomo

Click to expand...

Really ?
Around 300 services a year
Around 20 plugs replaced a year
The days of sooting up plugs were over by the 70's
Now my 1927 total loss motorcycles, yes their plugs need to be cleaned .
Can't remember the last time I had to clean a plug on the 150,000 mile a year L300.

Good to know Bert.

slomo