16 hp Vanguard engine shutdown
 

I turn the ignition key off. The engine continues to run for several seconds on one cylinder with the key off.

If I pull the right side spark plug wire, the engine will die immediately when I shut the key off. If I pull the left plug wire off, the engine will continue to run as if both plug wires are still on.

Looks like the ignition is shutting the spark off to the right side but not the left side. What's up?

does your vanguard have the electric fuel shutoff on the bottom of the carb?

Yes, I think that is what is shutting the engine down. The key switch is shutting off one cylinder, not the other. Does this mean the ground wire between the two cylinders is bad? I know the wire is connected to both coils and the ignition switch.

You have an issue with the kill circuit under the blower housing. Broken wire or bad diode. When you turn it off both mags should shut off right now. Fuel shut down is separate from the kill circuit, that is just shutting the engine off after it runs the carb passages dry.

I should look at a schematic so I don't make a fool of myself but does your key switch provide a ground in the off position ? if you have a broken wire so its not grounding when shut off

Yeah, the switch has a ground lead and it's working.

That's what I figured (diode). How do I check this?

Mike, a diode is nothing but a check valve. If you have a digital meter it should have a diode function on it to check it. If the wire is broken or the diode is open it will cause the issue you are having. If it is shorted it will cause the mags to kill each other and not run correctly. I had a shorted one on a 3165 and ordered 2 new mags but they didn't ship diodes with the new mags that I ordered so I made a trip to Radio Shack and picked these up. They are rated at 1.5 amps @ 1000 volts and their part number is 276-1114. I think they were about $2 or $3 for 3 of them. They have a mark on one end and that mark goes toward the mag. Here is a link on how to check them also. http://www.allaboutcircuits.com/vol_3/chpt_3/2.html.

Thanks very much guys. That's what I was looking for. I thought I had read that before here but couldn't remember.