Technical Question - Briggs Mower Engine

I got an old riding mower with a 11HP Briggs & Stratton engine. The mower runs fine most of the time, but every so often it starts to die, then comes back to a normal idle. However, under load this is worse and it can totally quit running. When it starts to die, it sounds exactly like I just shut off the key switch, not like it's running out of gas. (which has a different sound). I also noticed it does this more often when I am driving on rough ground.
I changed the spark plug, fuel line (which was getting soft) the gas filter, and made sure the carb bolts and all other visible bolts were tight. I also changed the oil, although I know that has nothing to do with the problem. I also tightened the spark plug wire end that snaps onto the plug. Then I started it and left it run at idle and in neutral. It ran for several minutes just fine, suddenly it started to die but came back in seconds. A minute later is did the same, and this continued at random. There is no pattern to it. One time it almost totally died.
Now, while watching it, I shorted out the screw where the wires join. One wire comes from beneath the engine cover / flywheel. The other wire goes to the key switch. When I shorted it to ground, it threw a spark and the engine started to die (exactly the same as the problem).
Now for the question. That wire that goes under the flywheel, I assume goes to the magneto. While this mower has a battery, I know the push mowers do not have a battery and have a similar setup. That leads me to question where is that power coming from. I know a magneto is a generator of sorts and produces the spark for the spark plug. But where the heck does that wire go? Like I said, when I short it to ground, it throws a noticable spark. Is that spark the same spark that is going to the spark plug? OK, now how do I test the power at that point to determine if the voltage drops or shuts off when the engine starts to die? Originally I was going to put a 12V tester (with built in bulb) across that connection screw to ground. But after thinking about it, I decided that the bulb would likely fry in a split second because the voltage is too high. Next, I considered my multimeter. but was afraid my meter would get fried since it does not have the capability to test anything over 1000V. So, I put a neon test light from that terminal to ground. The neon bulb did not light, so that tells me the voltage is not as high as I thought (the neon tester is designed for household outlet and wiring testing at 120 - 240 VAC.
That leaves me wondering what the heck to use to test that wire. Does anyone know the voltage at that point?
One other thing I should mention. If I move that wire which goes under the flywheel, the problem seems to vanish for a much longer time. Therefore, I am thinking there is a bad spot in that wire, but without ripping half the engine apart, I can not see that whole wire since it vanishes under the flywheel.
I'd much prefer to connect a tester before I start to rip the engine apart.
Can anyone help?
Thanks
Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

die,
out
were
do
snaps
to
join.
a
problem).
That
the
fry
considered
neon
light,
but
That wire is the kill wire, You ground it to stop the engine....if the insulation is worn or cracked it could intermittently touch the block or flywheel cover. You might be able to slip a piece of shrink tubing over it and slide it all the way up to the magneto.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You did not mention the air filter. If it is almost clogged bad things would happen.
LB
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.