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I have a 2004 Murray 42 riding mower with an 18.5 HP Briggs and Stratton (Model #31N707) that starts without a problem, runs with absolutely no sign of problems, then after about 8-10 minutes of mowing, it dies suddenly, and will not even turn over when I try to start it. If I let it cool for about 15 minutes and try to start it again, it will turn over, but won't start. If I try again the next day, it will start as if there never was a problem , then die suddenly after about 8-10 minutes of mowing, and the whole cycle starts again. It will die completely randomly, whether I am climbing a hill, descending a hill or on level ground. It also does not matter whether I am cutting through thick grass, or making turn on a part of the lawn that has already been mowed.

When I first checked the engine, I thought the problem was a the wire from the magneto to the spark plug had been chewed by a mouse that lived in the engine while the mower was in my shed over the winter. I replaced the magneto, replaced the spark plug, cleaned the air filter, and changed the oil.. It seemed to fix the problem, until it died suddenly and backfired a couple times after mowing about 8-10 minutes.

Because of the backfires, I thought the carburator must need cleaning. I took off the cup of the carburator and the pin assembly. The inside looked completely clean and pristine, so I did not go through the process of taking off and cleaning the entire carburator . Besides, I don't think that it is a dirty carburator because the engine runs completely fine until it instantly dies.

Besides the 電ead man switch under the seat, is there some other kind of kill switch that may be the source of the problem? Does anyone have any other ideas about what might be happening? Any help would be appreciated greatly.

Again in summary, this is what I have already done:
- Used fresh gasoline
- Replaced the spark plug and magneto/wire assembly
- cleaned the air filter
- replaced the fuel filter
- cleaned the cup of the carburator (it was so clean that I do not think that the rest of the carburator could be dirty enough to be the source of the problem)
- inspected the 電ead man switch under the seat no signs of problems

Is there a mouse nest in the shroud around the head? Sounds like its over heating.

Rob

Thanks for the reply, taxidermist.
Yes, there was an impressive amount of debris brought in by the mouse over the winter, but the first thing that I did was to remove everything. The only viable damage was the main wire between the magneto and the spark plug had a 2" section of the insulation around the wire completely chewed through. I replaced it, but the problem persists.

Will the engine stop suddenly and refuse to turn over if it is overheating? Maybe it is overheating for some other reason? What else could cause an engine to overheat? I just changed the oil, and cleaned the air filter (didn't replace it yet). I will take a close look for any other clogs or debris that I may have missed.

Well this seems to be a new one. I dont unstand how when it cuts out and u try and start it again the engine doesnt even turn over, yet ot does 15 mins later without starting. R u sure u took the blades out of gear and the machine was in neutral? If u didnt then the problem is fuel related - small blockage in fuel lines or maybe fuel tank breather blocked. Good luck

You may be dealing with multiple problems. You will have to get the problem to be evident and make some checks while the problem is happening. Make the problem happen and when the engine does not crank with the starter, see if you can rotate the flywheel by hand. Is there a click sound when you try to start the engine after it dies? We have to start somewhere and the problem(s) may be related.

Some of the ideas that come to mind that would cause your engine to die after 8-10 minutes could be a plugged fuel tank cap, ignition coil going open, wiring damage from mouse causing intermittent electrical problem. The no crank condition could be a separate problem so lets look at the no crank after it dies.

The problem with the no crank after engine dies condition prevents you from checking for spark so that's why I recommend looking at the no crank condition first.

Perform the above checks, answer the questions and report your findings.

Thanks a ton for all the replies. I will open it up in the morning and try your suggestions.
If the flywheel key was sheared, it would run a lot different and stall sooner than 8-10 minutes, right?

Pahl said:

Thanks a ton for all the replies. I will open it up in the morning and try your suggestions.
If the flywheel key was sheared, it would run a lot different and stall sooner than 8-10 minutes, right?

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A sheared flywheel key would cause the engine to be out of time in regard to spark timing, not valve timing, so the short answer to your question is yes. Usually a sheared flywheel key would cause a no start condition if far enough out of time or an engine that does not run properly and it would be all the time and not intermittent. Many times when an engine has a sheared flywheel key the engine will backfire as well.

I have the same engine does the same thing with a new coil a new $216.00 carb I have put carb and coil on Briggs 20 hp and it ran fine for as long as you wanted to run it. So I took it to a shop as much as I hate to spend money. They said the engine is fine but it still shuts off after a few mins.

Sent from my iPhone using LMF

Things to check when it dies

Will it turn over by hand from the crank pulley

When you hit your key do you have power at the starter

Also does this motor have a low oil alert ?

Rob

Cause was a pluged fuel cap causing a vacuum in the gas tank and no fuel flow. My cap has a very small vent hole about a 1/64",and was pluged, purged it with compressed air and problem solved.

RussellTP said:

Cause was a pluged fuel cap causing a vacuum in the gas tank and no fuel flow. My cap has a very small vent hole about a 1/64",and was pluged, purged it with compressed air and problem solved.

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It might be problem. Try to get new Fuel Cap.

It's been a while since I commented on this thread. Thanks to all who have tried to help. I've done all that everyone has suggested, except the new fuel cap, but the problem still persists, and today a new dramatic symptom arose. At about the same time as usual (about 10 minutes after mowing with perfect engine performance) as I was heading downhill, a sudden huge puff of blue-ish white smoke was emitted and the engine sputtered then the smoke went away when I came t level ground. I immediately disengaged the blades and turned the key to cut the engine. I assume that the smoke means that some sort of seal gave way and I am now burning oil. Any suggestions???:confused2:

Pahl said:

It's been a while since I commented on this thread. Thanks to all who have tried to help. I've done all that everyone has suggested, except the new fuel cap, but the problem still persists, and today a new dramatic symptom arose. At about the same time as usual (about 10 minutes after mowing with perfect engine performance) as I was heading downhill, a sudden huge puff of blue-ish white smoke was emitted and the engine sputtered then the smoke went away when I came t level ground. I immediately disengaged the blades and turned the key to cut the engine. I assume that the smoke means that some sort of seal gave way and I am now burning oil. Any suggestions???:confused2:

Click to expand...

It is possible that something "gave way" but it depends on how much of an incline you were going down and engine oil level at the time the puff of smoke happened. I have witnessed people going up a 50 degree incline with a zero turn mower trying to get the grass mowed and the same puff of smoke came out.

Check you oil and see if its over filled or you have too much from a carb leaking and filling the crank case full of fuel.

Also try adjusting your valves.

When you say it quits and will not turn over.....can you turn the motor over by hand? or is it locked up?


Rob

Is it possible that there is enough oil in the cylinder to cause hydro-lock? Letting the engine set allows it to drain out?

What does your plug look like when this happens? Is there oil on it? If you pull the plug, will it turn over then?

mine does the same thing, I put a hole in gas cap to let air in, but it still cuts off after 8-10 minutes

RussellTP said:

Cause was a pluged fuel cap causing a vacuum in the gas tank and no fuel flow. My cap has a very small vent hole about a 1/64",and was pluged, purged it with compressed air and problem solved.

Click to expand...

Seems I've read about this issue time and time again on this site ..... it may not be the cure in every case, but it easy enough to give it a try , sometimes we overlook the simplest things . Boobala :2cents:

Ok
We need to get to the bottom of this and to do that you need to make a few bibs bobs.

1) you need to buy an inline plug tester ( type with a neon tube in it ) or better still a colortune ( spark plug with a window in it )

When the engine stops whip the plug tester in & confirm you have a spark.
This eliminates a lot of safety switches the coil & module.

2) you got spark
Try some starter fluid in the carb.
If it goes and you can keep it running with little burst of starter fluid them the problem is in the fuel supply.


3) smoke is most likely a blown gasket but check carefully the level of oil in the sump, too much & too thin = duff float valve in carb.

Post the results and we can take it from there

I've been having this same issue with a 16.5 Briggs and it's currently dead back in the woods. I'm going try cleaning the gas cap and see if this will fix the issue. I think it may need a valve adjustment though. I will post my results. Thanks for the advise from those that use this site.

I had a prob that sounds similar to this. It was vapor lock in fuel system. Tried building a heat shield between the carb and block but that didnt do it. Finally I did away with the fuel solenoid by finding the same engine but different code and ordered the main jet and replaced the solenoid with it.. That took care of it.

Remove blower housing, top cover on engine, clean everything by hand & shop vac debris, no liquids or cleaners, a small nylon brush works well as does a piece of coat hanger wire for debris lodged in vanes on heads. Be sure to clean underside of blower housing as well. Check all electrical connections by hand including all ground cables & straps making sure everything is tight & secure.

I replaced the gas cap and so far so good.