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I have a 2019 Cub Cadet LT50 with a Kohler KT735-3076 engine with about 220 hours. After cutting a field for about an hour, the engine started choking and acting like it was starving for fuel. Pushing the choke forward solved the issue for about a minute, and the problem returned. I have only ever used ethanol-free gas.

I have followed the troubleshooting manual without success. Thus far:

Replaced spark plugs, fuel filter, and air filter.
Cleaned fuel lines into the tank and throughout
Rebuilt the carb (OEM kit)
Changed the fuel pump (OEM)
Tried an aftermarket carb (ruling out the solenoid)
Used fresh ethanol-free gas at each change from a fresh can.

Next up - fuel from a separate source and then ignition packs.

Any other suggestions would be very much appreciated.

Thanks!

BillCreighton said:

After cutting a field for about an hour,

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4 year old mower cutting field grass. Any tall grass being cut? Wondering if she is over heating?


Guessing a total clean is in order. Cooling fins first. Fuel tank, new fuel lines to carb and new filter.

Thanks for the quick reply. I should have also included that this is now happening in the workshop. I can’t keep the mower running for more than two or three minutes unless I keep throwing the choke on.

BillCreighton said:

Thanks for the quick reply. I should have also included that this is now happening in the workshop. I can’t keep the mower running for more than two or three minutes unless I keep throwing the choke on.

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You are not thinking straight. All the conditions matter not. Find out why she is not running proper. Hour meters matter not. Year of mower nothing. Where it does it......

You need air, fuel, spark and compression. Find out which one you are lacking.

BillCreighton said:

I can’t keep the mower running for more than two or three minutes unless I keep throwing the choke on.

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What does this tell you? She is thirsty......

A choke increases the fuel that enters a cylinder. Makes the air/fuel ratio richer. Cold weather or engine wants more fuel till she warms up to operating temp.

So what you are telling me is:

1.you need to dump and flush your fuel tank. Blow out with compressed air and SAFETY GLASSES.

2.Install all new fuel lines from tank to carb. Filter and a shut off valve would be nice.

3.Clean the carb. Remove the emulsion tube and all jets. Boil clean the sucker with a cheap hot plate and pan (less than 25 bucks).

4.Pressure test the carb needle at 7psi for an hour minimum.

slomo said:

What does this tell you? She is thirsty......

A choke increases the fuel that enters a cylinder. Makes the air/fuel ratio richer. Cold weather or engine wants more fuel till she warms up to operating temp.

So what you are telling me is:

1.you need to dump and flush your fuel tank. Blow out with compressed air and SAFETY GLASSES.

2.Install all new fuel lines from tank to carb. Filter and a shut off valve would be nice.

3.Clean the carb. Remove the emulsion tube and all jets. Boil clean the sucker with a cheap hot plate and pan (less than 25 bucks).

4.Pressure test the carb needle at 7psi for an hour minimum.

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If this engine has the Kohler smart choke on it, that might be the problem.

In the workshop, hook up some sort of alternative fuel tank even if you have to pinch the one off your push mower
If that runs fine then you probably have debris in the fuel tank blocking off the outlet
In any case let us know what happens

Okay this is going to be a bit of a long reply but before you go wasting a bunch of time with a lot of tests that may or may not be needed, waste a little time here reading. First, do as Bert mentioned.

If you can find a way to do it, gravity feed fuel directly to the carburetor from an alternative fuel tank. Go directly to the carburetor so you can eliminate all of the original parts of the fuel delivery system. Before you do that, disconnect the inlet side fuel line at the fuel pump coming from the fuel tank so you're not pumping fuel all over the place. See if the issue goes away. If it does, your carburetor and the rest of the engine components are fine. At this point you've proven it's a fuel delivery issue and now you need to figure out what it wrong somewhere upstream from the carburetor.

If you eliminate fuel filter, fuel lines and clogged fuel tank and the problem still exists, I would probably go to this next step if the rocker cover on fuel pump side of the engine is easily accessible just to rule out what I am about to go into.

Kohler had some issues with oil not draining back into the crankcase fast enough from the head on the fuel pump side of the engine due to the drain back holes not being large enough. That oil would block the pulses that cause the pulse fuel pump to work properly. This issue not showing up immediately when the unit was new would be highly unusual but if you've eliminated everything else, It would be worth a look.

Put everything back together as it would normally be. Run the engine until it starts acting up. Shut the engine down and immediately remove the fuel pump side rocker cover. Did a lot of oil run out? Maybe 1/4 cup? If so, that oil was blocking the pulses to your fuel pump and causing the fuel pump to not work properly. If you find this to be the issue, the fix it a 5/16" grease covered drill bit about a foot long to drill out those holes being very careful not to go too deep or your drill bit can hit a cam lobe. I think the service bulletin said to mark the drill bit 1-1/8" so you don't go to deep but I can't say for sure that depth is correct. Before you drill anything check back here and maybe there is a Kohler service tech on here that would still have their update book this issue was discussed in and they can verify the depth. If not, come back here and let us know and I'll find out. I didn't really plan on being on a forum answering questions when I retired so almost all of my reference material found it's way to the recycle pile.

I highly doubt this slow oil drain back is your issue. Like I stated those holes would have been too small from the factory and this engine should have had this issue from new. But if you rule out everything else it would be worth a look.

Thanks, guys, for the great advice. I was able to get fuel from a separate tank and confirmed the carb and engine were ok. With the tank, hoses, filter clean, and a new fuel pump, that left the pulse tube on the rocker cover. Pulled it and blew out a wad of black sludge. I put it back on before pulling the cover, and the engine ran fine, almost. While the fuel problem was resolved, the engine was not firing properly - a weak coil. I replaced them both, and it fired up and now runs like new. About five hours of run time in, still no sign of problems. If/when it starts acting up again, I'll pull the cover and check for excess oil as above - now that I know what to look for.

Many thanks and all the best

Thanks very much Bill for coming back with that
It is some thing I have never come across before but from now I will look for
Glad yo got it sorted now go mow .

Wanted to say thank you for this thread. Was having problem with my mower also, similar to what was described. I replaced the fuel filter, air filter, spark plugs and fuel pump and cleaned/rebuilt the carb. Did not see a single speck of dirt in the fuel tank. Symptoms where that after running awhile and once warmed up anytime I hit an incline, regardless of how minor, the tractor sputtered and died. I decided to empty the fuel tank and replace the fuel lines as a last ditch effort before buying a new carb. When I disconnected the fuel line from the tank to the fuel filter I noticed the fuel was barely dripping out, I blew into the line and it blew out what was left of a bug into the fuel tank. Long story short although the tank was clear and fuel was flowing it was restricted by the bug's body and I'm guessing it just wasn't enough fuel to pump when hitting a hill. Running like a dream now.