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