PT-425 Run-on

Impulse · Jun 16, 2022

I have a PT-425 with the Subaru in it. My problem is that in order to get the engine to shut off, after I turn the key off, I need to turn on the lights. It makes me think that the ignition is still letting enough juice through to keep the solenoid open and the draw from the lights drops it down to kill it. I haven’t metered anything or really done any type of diag but was wondering if I could take a shortcut with someone having already experienced this.

Any thoughts? Thanks!

Tchamp · Jun 17, 2022

Impulse said:
I have a PT-425 with the Subaru in it. My problem is that in order to get the engine to shut off, after I turn the key off, I need to turn on the lights. It makes me think that the ignition is still letting enough juice through to keep the solenoid open and the draw from the lights drops it down to kill it. I haven’t metered anything or really done any type of diag but was wondering if I could take a shortcut with someone having already experienced this.

Any thoughts? Thanks!

Mine quit shutting off from the switch, but the electric fuel cutoff on the carburator works, and i also have an electric fuel pump on it as well. It takes a few second’s but shuts off with the key off. I need to replace the diodes to allow the switch to kill it but dont want to remove engine hist for that, when i can rely on the fuel shutoff for now. When the. Time comes to do any other major work requiring the engine to come out, its on the list! Lol

Lnk · Jun 17, 2022

Impulse said:
I have a PT-425 with the Subaru in it. My problem is that in order to get the engine to shut off, after I turn the key off, I need to turn on the lights. It makes me think that the ignition is still letting enough juice through to keep the solenoid open and the draw from the lights drops it down to kill it. I haven’t metered anything or really done any type of diag but was wondering if I could take a shortcut with someone having already experienced this.

Any thoughts? Thanks!

Throttle it down to a low idle, count to ten and turn off the key. I am not sure why the robin engine does this. But that has worked for me. Good luck.

Impulse · Jun 19, 2022

Thanks for the response. I have tried throttling down but that doesn’t solve the issues. I can turn it to off, take the key out and it will continue to run and I used to try choking it out but hit the lights one time and it killed it instantly so that is what I’ve done since. That makes me think something electrical is going on.

Impulse · Jun 19, 2022

Tchamp said:
Mine quit shutting off from the switch, but the electric fuel cutoff on the carburator works, and i also have an electric fuel pump on it as well. It takes a few second’s but shuts off with the key off. I need to replace the diodes to allow the switch to kill it but dont want to remove engine hist for that, when i can rely on the fuel shutoff for now. When the. Time comes to do any other major work requiring the engine to come out, its on the list! Lol

I’m not familiar with the diodes for killing the engine. If that is the issue and requires pulling the engine, I’ll probably stick with the light switch. Thanks

BobRip · Jun 26, 2022

Do the lights actually work when they are turned on?

Impulse · Jun 27, 2022

The lights work with the key turned on but do not light when the key is turned off. That one has me at a loss as to why it helps/affects the engine stopping then with the key off.

If I have the lights off with the engine running and turn off the key, the engine will run-on for a significant amount of time (30+ seconds)

If I have the lights on with the engine running and turn off the key, the engine will stop immediately.

If I have lights off with engine running and turn off the key, the engine will run-on but immediately stop if I then turn on the light switch.

Thanks!

ponytug · Jun 27, 2022

Impulse said:
The lights work with the key turned on but do not light when the key is turned off. That one has me at a loss as to why it helps/affects the engine stopping then with the key off.

If I have the lights off with the engine running and turn off the key, the engine will run-on for a significant amount of time (30+ seconds)

If I have the lights on with the engine running and turn off the key, the engine will stop immediately.

If I have lights off with engine running and turn off the key, the engine will run-on but immediately stop if I then turn on the light switch.

Thanks!

I suspect that you have an electrical gremlin. Surprise! With the lights on as you turn the engine off, you have a better short to ground from your +12V side, which shuts the fuel flow off ASAP. To test it, I would get a jumper cable, and jump the negative battery cable to the engine and see if it helps and then try to jump the negative to the front frame. Or just double check all of your grounds; battery cable (both ends), and the cable itself for corrosion, and any grounds from the engine to the rear frame and rear frame to front frame (I added a bunch of ground paths, all tied to a single point on the engine when I got my PT, so I forget where the factory grounds are.)

Or just remember to leave a light in for us...

All the best,

Peter