Troubleshooting a new-ish Riding Mower engine

Factual Questions
1

Hi all,

While this might not be the “best” place to ask these questions, I figured many of you would have practical experience that might help. Topic: one year old riding mower. Craftsman, 19.5 hp Kohler engine. Used for two summers. At the end of this summer, it has gotten into a state where it won’t stay running. I’ve tried:

  • Annual maintenance type stuff, like change oil and filter, change breather element.
  • Possible carb issues: Put in fresh gasoline and put some carb cleaner in it.

During my last attempt to fix it, about 2-3 weeks ago, it would run for 20 seconds repeatedly, then quit. I didn’t let it sit long between tries. The battery started to flag, so I let it sit a while and got busy with life.

It is sunny and warm today, so I tried again. This time, it ran for fully 40 seconds before quitting, and now the battery is dead and won’t crank the starter. So I headed to Menards to get a 1A charger, and connected it. It’s currently sitting in the garage, awaiting the next wintery blast.

OK, so, for it to run a while and then quit, my feeling (and I’m a newbie with regards to small engines) was that I’m seeing fuel starvation, that it can’t flow fast enough to the carburetor. Hence, I purchased a new fuel filter. But I haven’t swapped it out yet: I don’t want to fire the “parts cannon” blindly at the problem without further study.

The old fuel filter doesn’t seem all that dirty, but I dunno. My spouse (the primary driver of the mower) has a habit of letting dirt and bugs, etc. go into the fuel tank during the summer when she refuels it, then she said she ran it dry at the end of the season. That may have moved the debris into the filter, en bloc. But could that be blocking adequate fuel flow alone? Maybe…

Meanwhile, many other websites say to clean out the carburetor. With a spray can of some kind of volatile, no doubt. But if the engine runs for fully 40 seconds, could the carb jets really that dirty? Could that be it?

Thanks in advance for your wisdom!

2

I had a similar problem and replaced the whole carburetor. It wasn’t terribly expensive and after I cleaned it I now have a spare. It seems it’s not a problem with the jets plugging up but the float inlet getting clogged. It will let enough fuel through while off to start and run for a bit (fill the float bowl) but not a fast enough flow to keep running. I figured keep a spare on hand cause if it happened once it will again. And yes change the filter too.

3

Sounds very much like an “inadequate fuel flow” problem. You could verify this by getting the engine started, then dribbling fuel (not much - just drops) into the air intake when it starts to die: if this keeps it running, diagnosis is confirmed.

You then do such things as change the fuel filter, check for kinks in fuel lines, dissect & clean carb, etc.

4

It does sound like it’s a fuel problem. Does it use a fuel pump or is it gravity-fed? You’ve replaced the fuel filter already? Can you see what the fuel flow is like, either by allowing the fuel to flow from the fuel line at the filter or by cranking it to run the fuel pump? You can use a jar or similar container to catch the fuel. If you remove the plug(s), the battery will keep turning the engine much longer so the fuel pump (if you have one) runs.

Same thing at the carb. Can you open a fuel drain on the bowl? Can you remove the bowl itself? In both cases, you want a steady stream of fuel.

There are lots of other possibilities. Is there a solenoid to cut off fuel in the carb bowl? This SHOULD fail open so fuel flows to the jets, but there might be an issue with the wiring.

Finally, maybe you can hook a piece of fuel line directly to the fuel input on the carb. Hold it straight up and fill it with fuel. See if the engine will run and use all the fuel in the piece of fuel line. If it does, the problem is probably in the fuel system prior to the carb (i.e., debris in tank, bad pump, clogged filter, or something else).

5

Quick, easy one to try:

It may have a vented fuel cap. The vent could be clogged. Try removing the cap and starting the engine. If it runs as expected, you probably just need a new fuel cap (or figure out if it can be cleaned with compressed air or carb cleaner)

6

You are running out of fuel for some reason. There is no fuel pump on these engines, it is gravity fed.

The carburator has a needle valve to keep the thing from getting too much fuel. Sometimes the needle valve will stick open after the engine is shut off, causing all of the gas to drain into the bottom of the engine and into the oil. I had to install a cut-off valve to keep this from happening in a previous mower.

It sounds like your carb has the opposite problem and is not allowing gas into the engine, so it is running on the gas that is in the carb until it runs out. Carb float and needle vavle is not working as it should.

7

Agree with the others.

Replace fuel filter, check fuel cap, etc. If it still does it, simply replace the carb. It shouldn’t be too expensive, and if you’re even moderately handy it shouldn’t be a difficult job.

8

Thank you, next up I will:

  • Check cap vent
  • Replace fuel filter (and let fuel flow out thru line which itself might be clogged with bugs and dirt)
  • Put focus on the carb inlet

Cheers!

9

One thing to keep in mind: most mowers do not have a fuel pump, and thus are gravity-fed. When you disconnect the fuel filter, the entire contents of the fuel tank will want to empty through the hose. Here’s what I do:

Put on some nitrile exam gloves. (When I work with gasoline, I will sometimes put two pair on each hand.) You can buy these cheap at Harbor Freight.

Apply a small amount of oil to each end of the new fuel filter. This will make it easier to fit the hoses onto the new filter.

Grab two pair of pliers and a jar.

There should be two hose clips, one on each end of the fuel filter. For each hose clip, squeeze the tabs using the pliers, then move the hose clip further down the rubber hose, away from the fuel filter.

Grab onto the fuel filter with one pair of pliers. Use the other pair of pliers to twist (not pull on - twist) each hose relative to the filter where it attaches to the filter. This will “break free” each hose.

The next steps are easier with two people, but can be done by yourself if you do things quickly:

Disconnect each hose from the filter by pulling and twisting on it. A small amount of fuel will run out for the hose connecting to the engine, while the hose connecting to the fuel tank will allow fuel to run until the tank is dry. Have the fuel run into the jar. Let it drain for a few seconds. Make sure it is free-flowing for the hose that connects to the fuel tank.

If a second person is helping, have them put their thumb over the opening in the hose that goes to the fuel tank while you’re attaching the other hose to the filter.

Quickly install each hose onto the new fuel filter. Use pliers to secure clamps onto it.

With some mowers, there is enough slack in the hose between the filter and fuel tank that you’re able to lift the filter an inch or two above the fuel level in tank. Which is nice, obviously, since it means gas will not run out (other than the small amount of fuel between the engine and filter).

10

Check inside the tank, the outlet might be clogged.

11

I’ll be letting some fuel flow thru the line leading to the filter, into a bottle, to see what kind of junk might be clogging the line. I have a small vice grip to clamp the line shut.

I previously managed to fix a fuel flow problem with a push mower and much smaller fuel tank by “cleaning” the fuel and agitating (using a turkey baster) the fuel in the tank, then passing it through a coffee filter and re-using it. Worked great; I’m convinced that paper filters can help clean gasoline. (The element in the OEM fuel filter looks like cardboard.)