Briggs and Stratton 104M02-0010-F1 starts 1st pull runs and mows perfectly about 15 minutes and dies. Won’t restart until next day. Please help

[slomo]

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

Ding Ding Ding, we have a winner folks LOL.

 

[Hammermechanicman]

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.

 

[Rivets]

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.

 

[Hammermechanicman]

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.

 

[Rivets]

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

 

[Hammermechanicman]

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.

 

[sgkent]

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.

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

 

[Gord Baker]

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.

 

[sgkent]

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.