Briggs and Stratton engine refusing to stop...

[Jules]

Grrr. I got the B+S engine in the mower running (10HP sidevalve with key start) - and then found that when I turn the key to shut it off, the engine happily carries on; the only way to stop it was to pull the lead for the spark plug off.

This particular engine has a magneto mounted beside the flywheel for spark generation. There's a thin black wire which runs down from it to an insulated post on the side of the engine, and from there a wire which goes up to one of the terminals on the back of the keyswitch.

The wire seems to serve no useful purpose, which is presumably my problem ;-) Regardless of ignition switch position it does nothing - neither showing a voltage nor connecting to chassis ground.

I tried shorting it to ground when the engine was running, but that didn't work. Maybe it's supposed to give +12V with the ignition *off*? (I'm reluctant to try that just on the offchance)

Any ideas?

cheers

Jules

[R]

No earth at the switch resulting in no short circuit to earth on the LT side to stop engine

[AlanD]

He's tried shorting to ground already however. I'd say the other end of the wire (magneto end) has become disconnected, or that there is an internal break in it.

[Fredxx]

If there's a bolt close to the plug, I'd be tempted to cut a strip of metal which is shaped and of sufficient length to short out the plug when pushed onto it, as seen in many old lawn mowers.

[RobertL]

LT side? i thought these things had no LT side and worked by having the magnet whizz past the coil and generate the HT directly from that. My old B+S had a strip of bendy metal bolted to the housing next to the plug which you pressed onto the top contact of the plug when you wnated it to stop.

Robert

[Rob G]

I'm not sure how you switch off a magneto system with a key, but it certainly sounds as if one of the wires from the insulated post is no longer doing it's thing.

My 40 year B &S has the bent strip on the cylinder head as mentioned above.

Rob

[Jules]

Yes, that occurred to me after I posted (it had been a long day!) - I'll plonk the meter on it later and check that out. The odd thing though is that the wire running down from the keyswitch to the post on the engine seems to be bad too (either the wire or keyswitch, or switch ground as someone mentioned) - but then this mower does seem to be posessed and loves throwing multiple faults at me, so I wouldn't put it past it ;-) cheers

J.

[Jules]

And the result was... multiple faults. Bad (intermittant) ground between the chassis and the metal cowl which supports the instruments / switch / steering wheel, *and* a break (intermittant) in the wire running from the magneto to the side of the engine.

cheers

Jules

[Gib Bogle]

Ah, yes, a wire is not the same as a connection. Plastic insulation can hide a multitude of sins.

[meow2222]

very effective way to teach kids to pay attention

NT

[Jules]

Indeed. The insulation around the wire looked good, but there was a break just downstream of the connector on the side of the engine.

Two days ago I made a new bracket for part of the mower deck as the original had buckled (resulting in blade slip under heavy load). Then yesterday I made a new throttle cable and put on a new silencer (along with some homebrew metalwork to secure it much better than the original design). It now cuts beautifully and isn't deafening! :-)

cheers

Jules