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My wife bought this Toro mower used. As stated above, it starts first pull, runs, and mows perfectly for about 15 minutes then just dies. It sounds like the motor slows down right before it dies. The next day same story. Starts runs about 15 minutes and quits. I have cleaned out the carburetor and fuel tank. Changed the spark plug. Blown out the air filter. I have read that you can’t really get good readings on the coil with an ohmmeter, but for info purposes mine reads 9.70.
Thank you
Phillip

Next time it happens check to see if you have spark. Sounds to me like you have a hot short or hot open, which would indicate a bad coil.

Will do. Thank you

One thing to try is loosening the gas cap. At times, the breathe hole gets clogged, and once enough fuel is used, a vacuum is created, and the fuel won't flow. Just a random thought.....

someone here has recommended a spark tester from HF. That is one way you could see if you have spark. I know of 3 issues that are heat related - bad coil, tight valves / loose head, and fuel starvation if the tank can't breathe.

Bad coil - test for spark
Tight valves or loose head - check compression before and when it happens to compare
Tank not breathing - loosen the cap and try again.

Those inline spark testers are a waste of money. Yes you will see a light flicker if you have spark, but.......

Coils need to be LOAD tested. As in this tool or something like it.

Sorry Slomo, but you and I disagree on this one. Been using the inline neon light tester since the mid 70’s and I’ve never had a problem. I’m probably on my 5th or 6th one. I don’t remember ever needing to know the sparks strength, just if the system is sending enough current to jump the gap when the plug is in the cylinder.

the only time an inline tester would not be accurate would be if the plug was grounded internally, tip crushed, carbon across the gap etc.. If the spark jumps the gap that is enough to know there is spark. The gap and compression in the engine determine the actual firing voltage of the plug.

Sgkent, I need to be clearer, testing a plug outside the cylinder can give you a false reading. I’ve used a tester on plugs without them being installed in the cylinder and they will fire. Once the plug is installed it may no longer jumped the gap. It’s happened to me more than once.

Rivets said:

Sorry Slomo, but you and I disagree on this one. Been using the inline neon light tester since the mid 70’s and I’ve never had a problem. I’m probably on my 5th or 6th one. I don’t remember ever needing to know the sparks strength, just if the system is sending enough current to jump the gap when the plug is in the cylinder.

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WIth the PET-4000, you see the actual spark and know if the coil is strong enough for combustion. You guys only see half of the puzzle.

Rivets said:

Once the plug is installed it may no longer jumped the gap. It’s happened to me more than once.

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Ding Ding Ding, we have a winner folks LOL.

The 2 different testers will tell you different things. The inline neon tester will tell you if the coil can discharge through the spark plug. It does not tell you is the plug is good or not. The plug can be shorted with carbon fouling and the neon tester will still light. It won't tell you what the reserve capacity of the coil is. Just that it has enough energy to fire with whatever gap is present at the plug. A gap type tester can be used a couple ways. The first way is to connect from coil lead to ground. If the coil can fire across a 1/4" gap it has enough energy to run any small engine. Some testers have an adjustable gap so you can widen the gap that will test the coils energy capacity. As an example Echo says to open the gap to 6mm (.243) to test if coil has enough capacity. Pretty much a quarter inch. You can also connect the gap tester from coil to spark plug and it will tell you the same as the neon tester with the exception that it also tests that the coil has enough reserve capacity. Testers don't check the condition of the spark plug.

Good point, but the average Joe really has no need for that tester, nor will understand what you are saying. I do have one in my tool box, but don’t ask me the last time it got taken out.

I have both and use them for different things. I use a pair of inline neon testers on twins checking for intermittent bad coils. For just checking for spark i use the briggs tester. If it jumps the gap i have good spark.

I hope we’ll all agree to disagree and solve the OP’s problem.

Ok. Back on the problem. Start and run the mower until it stops. Remove the spark plug lead and hold it approx 1/4" from ground and pull the rope. If a spark jumps the gap it is not a spark problem. If no spark it needs a new coil. If it has spark after it it dies and won't restart remove the air cleaner and spray some starting fluid or carb cleaner into the carb and try to start mower. If it fires off for a few seconds it has a fuel delivery problem.

Rivets said:

Sgkent, I need to be clearer, testing a plug outside the cylinder can give you a false reading. I’ve used a tester on plugs without them being installed in the cylinder and they will fire. Once the plug is installed it may no longer jumped the gap. It’s happened to me more than once.

Click to expand...

very true. The compression raises the firing voltage needed to jump the gap.

Try a properly gapped New Spark Plug. I believe you have a fuel delivery problem if it runs for 15 minutes.
Try starting with Fuel Tank Cap removed, then replaced. New filter installed at correct orientation.
Remove float bowl, clean and inspect. Fuel should flow freely when bowl is removed if it has a gravity feed.

15 minutes in my opinion rules out the fuel system unless the fuel filter is clogged so once the fuel in the bowl is used up it takes time to refill. But it could be a choke sticking or even a plugged up air filter that causes the mixture to be too rich when hot. I had a friend who could only mow about half her lawn before the mower died. It was a dirty air cleaner that caused the mixture to be too rich when hot. Making matters worse she left it outside so the filter would get wet and that caused issues too.

Other time issues could be a coil heating up and opening, a head gasket that leaks more when hot thus lowering compression, or tight valves that expand and stay slightly open when hot.