I have a John Deere LX 277 lawn tractor that has developed an engine problem that has my mechanic and me stumped. The motor in question is a Kawasaki FH500V (electric starter).

While the engine is cool, it works fine, with no problems starting it and normal power output. Once the engine warms up, it starts to stutter and die, especially during variantions in power demand as in turning from uphill mowing to downhill (and vice versa!) or engaging the mower deck. When it starts to stutter, sometimes one can "rescue" it by engaging the choke, but not always. After it died, it can be re-started with 5-10 seconds of starter applied.

After the engine developed the problem my first reaction was to checkintake the fuel line, fuel filter, air filter and fuel pump. All of those were Ok, though. So I took the mower to the mechanic who re-checked the same things and also found them to be Ok. He also checked the carburetor with no problems found. The mechanic was advised by John Deere to replace the ignition coils (the motor uses two separate coils for its two cylinders), which was done, but without success.

Since the mechanic seems to have run out of ideas, I started to fiddle with the engine a bit. One thing I noticed is that, with the air filter off and the carburetor intake in plain sight, one can see a fine mist of fuel being ejected from it while the engine stutters. So there seems to be air travel in the wrong direction, at least during some parts of the cycle. Something else that I noticed is that the intake manifold (part A in the second photo on Page 70 in the linked PDF) is metallic clean on the end for one cylinder but kind of sooty black on the other cylinder's end.

From those observations I've deduced a working hypothesis, that something about the intake valve on the "sooty" cylinder might be wrong sending some exhaust into the intake during some part of the cycle. I've adjusted the valve clearance as explained on page 32 to no avail. The next step would be to disassebmle the cylinder head and inspect the valves themselves. Either related to improper sealing of the valve or valve timing. This, however, is somewhat outside my comfort zone, as I am just a computer software guy. Can someone with more gasoline running in their veins maybe advise me on how to proceed and whether my hypothesis makes sense or I am barking up the wrong tree?

  • I would normally suggest your issue is a carb issue. It only takes three (external) things for a gasoline engine to run: air; fuel; ignition source. (Note: some will argue an engine needs compression as well ... not going there). If your engine is slowing down after a period of time, it has air and spark. This leads me to believe it's fuel related. Just thinking outloud. – Pᴀᴜʟsᴛᴇʀ2 Oct 5 '15 at 23:23
  • Yes, that's what I originally thought, too. However, the mechanic having checked the carburetor and the fact that fuel is being ejected (!) from the inlet side of the carburetor when the motor stutters made me look for other theories. – hennejg Oct 7 '15 at 16:53
  • Don't forget to award yourself the answer :) You'll get a badge for it – DucatiKiller Dec 22 '15 at 22:02

To answer my own question: I contacted another mechanic with this issue who fixed it in no time. I feel quite stupid now...

The problem was indeed with the fuel line. The fuel line was clogged with some bits of grass that had fallen in during refilling. But it was clogged in such a "creative" way that the fuel pump was able to pull some fuel through it before it closed up like a valve, giving the impression that everything was fine upon inspection. sigh

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  • That's brutal. Lessons can be quite painful. I've had a few that are on par with this one for sure. – DucatiKiller Dec 22 '15 at 22:02

This sounds like a defective fuel cap. This is a problem with the LX288 / 277 the vent hole clogs and you get a vacuum lock situation.

Replace that cap!

Also, less likely is sticking valves, which occur when the engine gets hot. Again a known problem with the FH500V engine.

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  • Thanks for your idea, Jack, and an excellent reference for other folks with similar problems. However, it was indeed the fuel line as answered by myself above. – hennejg Jun 9 '16 at 9:56

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