ST-480 Workhorse refuses to shut off with pedal released

[Swanny85]

Hello all!

First of all, I have searched this board and found quite a few threads for this same issue, tried suggestions or inspections recommended in those threads with no results. This one's a stumper for me.

I'm working on my father in law's ST-480, I believe it's a 2003 (Date code: M2703) with the Briggs and Stratton engine. He says almost a year ago while he was using it the engine just didn't turn off when the pedal was released. Key off, still running. Disconnected the battery, still running. He even says he ran it into the side of a building trying to stall it which of course didn't work but it sounds funny. He eventually pulled the fuel line off and waited for it to starve and shut off.

So being the curious guy I am (and a glutton for punishment) I throw a battery in there and fire it up. Yep, sure enough it won't shut off.

I checked continuity through the pedal switch on both circuits, I have continuity to ground on the white wire only when the pedal is released. The white wire goes down to the engine compartment and looks like it has a spade connector and round connector. Spade isn't hooked to anything, the round one goes to a magneto (I think). So, easy peasy, the magneto P wire isn't getting grounded for some reason, right? I strip back the insulation just a couple inches from the magneto, clamp a test lead to that wire and touch to ground .... engine keeps running.

I try a different part of the chassis, still running. I wire brush the negative terminal of the battery and touch the lead to the terminal/post, still running. I check resistance of my test lead, 0.1Ω.

So one of the possibilities is a stuck solenoid for the starter/generator. I leave the fuel line disconnected, get on and off the accelerator, and the engine spins with the pedal down, stops spinning with it released. Solenoid doesn't seem to be sticking. Disconnecting the fuel is the only way to shut the sucker off.

I have not pulled the wire off a spark plug with the engine running yet, but the only thing that makes sense to me is a bad connection within the magneto to the "P" wire to ground primary. But I've never seen a magneto do this before so I'm hesitant to pull the trigger on one. Is there a way to test this theory? I tried measuring voltage on the "P" wire and got about 20v DC with the engine running, 2v while cranking with fuel disconnected.

Also, does anyone have the model number for the Briggs that is in these guys? Maybe I'm blind, but I wasn't able to find an engine code anywhere on the cart or engine itself.

Thanks you any assistance! (and for reading this far if you have)

[cart around]

I didn't know that you could get a 2003 with a Briggs, but this thread says yes. https://www.buggiesgonewild.com/showthread.php?t=23037

If it's an actual magneto system, the only way to shut one off is to ground out the ignition system. Either at the spark plug, or the points. I don't know if a pointless magneto exists, so now I have to research.

Parts diagram here. https://www.jackssmallengines.com/ja...303440-1410-e2

[CP241]

I was unaware there was a Briggs also.

But if its anything like a club car or any other type system with a self contained motor (predator, vanguard, etc) there should be a kill wire going to the ignition coil. Or a "stop relay" like yamahas have. You ground the wire and it kills spark, shuts off the engine. I'd guess theres a microswitch or something somewhere that sends ground to that wire when you release the pedal that has either come disconnected or gone bad.

This is just thinking out loud and throwing a dart in the dark, but I cant think of anything else off hand. Just look for a wire coming from the ignition coil area. Pictures may help, most of us have never seen this configuration before but I'm sure it cant be too difficult to figure out.

[kgsc]

St480 was a workhorse with the Briggs engine. Turned into a 1500x. Never got into this part of mine but it was a pedal stop/start which implies a micro switch at the pedal to ground the ignition. There is a kill wire which may have come undone but would look at the switch.

Manual is here https://www.buggiesgonewild.com/showthread.php?t=1902

[CP241]

Originally Posted by kgsc

St480 was a workhorse with the Briggs engine. Turned into a 1500x. Never got into this part of mine but it was a pedal stop/start which implies a micro switch at the pedal to ground the ignition. There is a kill wire which may have come undone but would look at the switch.

Manual is here https://www.buggiesgonewild.com/showthread.php?t=1902

[Swanny85]

Well, things seem to have gotten a little stranger.

So, I confirmed that the white wire I was concentrating on does go to the primary coil on the magneto. I used an ohmmeter and measured from the spark plug wire to the engine block and got 4.95 ohms, got the same measurement from the plug wire to my white wire. So, on a whim I jumped my white wire to ground and tried to start the engine. It cranked without starting. I cranked it for a long time, no start. Then while it was cranking I disconnected my jumper to ground and boom, she fired up. No sweat, connect to ground again and ... it won't shut off.

Kinda losing my mind here. I want to say there's a bad connection from the kill wire to the primary coil, because that's the only thing that makes sense, but I've never heard of a magneto/coil failing on the "stuck on" sense.

I attached a picture of said white wire as well as the jumper configuration where the engine would not start. With the engine running, I put the wire back in the same spot and she stays running. So at least I know I have the right wire and I know it's ignition, but dang if it's not strange.

[kgsc]

Well found some information on the 800 but think it is close. Look here https://www.manualslib.com/manual/15...age=134#manual

Looks like there is a relay next to the solenoid