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 “dead 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 “dead man” switch under the seat – no signs of problems