We have a Scotts 21" walk-behind mower with a Briggs & Stratton 6.5hp
OHV "Intek" engine (with primer and auto-choke).
One day it suddenly would not run for more than about a minute and then
quite. Started up fine after priming; but, then soon stopped.
I figured, "Uh, oh; the carburator must have gotten gunked up because
we were running it without the paper part of the filter. Tried cleaning
the carburator-- no change.
Finally got a new carburator and a new filter. Didn't help. Maybe the
gas cap vent was clogged up; so, tried drilling a hole in the cap to
make sure it would feed gas to the engine; didn't matter. Drained out
old oil and replaced it; same thing.
Then, after reading some stuff on the B&S site, it seemed like a good
idea to check if the spark plug was wet or dry after the engine
stopped. That way, when I asked for help, I could include that info.
So, I remove the spark plug and notice I'd somehow managed to break it
during removal. Rats! (BTW, the plug did not seem especially wet or
Checking through our junk, there turned out to be a plug that was a bit
longer but had the right threading and internal length. So, after
matching the gap, in went the replacement plug.
I started the mower to make sure it would run the usual minute or so
with the new plug. It ran fine. In fact, it kept running. The mower was
My guess is that the old plug had developed a fracture, which is why it
broke so easily during removal. Evidently, after running for a little
while, heat led to expansion and a separation in the conductive path
inside the plug and it just stopped firing-- nicely mimmicking a fuel
flow glitch and other assorted problems.
Maybe a fractured spark plug does not explain your 'engine stops
running' mystery. But, if it does, finding the problem at the start can
save money and a bunch of bother.