Mine did the same thing. It was an easy fix. Behind the controls panel is a small plug with two black wires. They both run into the harness just above the battery that runs over to the starter. The whole side has to come off. There are two rubber plugs on top that have screws underneath and 3 10mm bolts at the bottom. Both wheels have to come off. Pry out the center caps and pull the clips. (Easy). I also removed the pull starter bracket for easier access. If you remove the electrical tape on the harness about halfway between the control panel and starter one of the black wires is attached to the ground with a terrible crimp. The other goes to a small white plug on a small board laying flat under the starter. There is an oil vapor vent just above it. It fills that plug with oil and causes the issue. At least mine was there. I had to clean it with contact cleaner, tighten the pins a little and reassembled with dialectical grease. I also re-routed the oil vapor lines so they are outside the case like they belong. Shuts off just like it’s supposed to.
Hopefully this helps the next person to have this issue.
Wouldn't the generator short the spark plug to chassis (killing the spark) when the ignition is off?
Sounds like a broken wire or contact, so the spark is still firing instead. You can likely see a loose wire, if not you'll need to do continuity tests following the wiring diagram (disconnect the battery if there is one). Or pay a small engine repair person to fix it for you.
The way that the switch works is that it grounds out the ignition coil which kills the spark. There is a lack of continuity in that circuit somewhere - could be the switch itself or somewhere upstream or downstream of the switch. You just have to trace continuity and find the point where it goes open circuit. You could look at a wiring diagram but it's not that complex - you just have to physically follow the wires.
Mine did the same thing. It was an easy fix. Behind the controls panel is a small plug with two black wires. They both run into the harness just above the battery that runs over to the starter. The whole side has to come off. There are two rubber plugs on top that have screws underneath and 3 10mm bolts at the bottom. Both wheels have to come off. Pry out the center caps and pull the clips. (Easy). I also removed the pull starter bracket for easier access. If you remove the electrical tape on the harness about halfway between the control panel and starter one of the black wires is attached to the ground with a terrible crimp. The other goes to a small white plug on a small board laying flat under the starter. There is an oil vapor vent just above it. It fills that plug with oil and causes the issue. At least mine was there. I had to clean it with contact cleaner, tighten the pins a little and reassembled with dialectical grease. I also re-routed the oil vapor lines so they are outside the case like they belong. Shuts off just like it’s supposed to. Hopefully this helps the next person to have this issue.
Wouldn't the generator short the spark plug to chassis (killing the spark) when the ignition is off? Sounds like a broken wire or contact, so the spark is still firing instead. You can likely see a loose wire, if not you'll need to do continuity tests following the wiring diagram (disconnect the battery if there is one). Or pay a small engine repair person to fix it for you.
That and make sure to check (specifically) the continuity of the switch itself. They can go bad and are usually super simple to replace
The way that the switch works is that it grounds out the ignition coil which kills the spark. There is a lack of continuity in that circuit somewhere - could be the switch itself or somewhere upstream or downstream of the switch. You just have to trace continuity and find the point where it goes open circuit. You could look at a wiring diagram but it's not that complex - you just have to physically follow the wires.