Mower won't stop

[fred]

Its an Electrolux Partner 12 wheeled strimmer. Only way to stop it is to pu ll the spark plug lead. Its not a question of adjusting the bowden cable as I tried that. There appears to be some sort of electronic gubbins at the m otor end of the cable. Had a quick luck but its beyond my boy scout capabil ities. Have to get it sorted as the spark plug lead/cap is not taking kindl y to being pulled on and off regularly. Any suggestions would be helpful be fore I take it to my local dealer whose hourly rate is more than BMW charge for service and he is working from a shed at the back of his house.

[newshound]

In the old days before plug caps were invented, and the plug lead was connected directly to the plug via a nut and a couple of washers, quite a few "magneto" engines had a springy steel strip attached to one of the cylinder head bolts which you just pushed into contact with the high tension to stop the engine.

[Muddymike]

Its an Electrolux Partner 12 wheeled strimmer. Only way to stop it is to pull the spark plug lead. Its not a question of adjusting the bowden cable as I tried that. There appears to be some sort of electronic gubbins at the motor end of the cable. Had a quick luck but its beyond my boy scout capabilities. Have to get it sorted as the spark plug lead/cap is not taking kindly to being pulled on and off regularly. Any suggestions would be helpful before I take it to my local dealer whose hourly rate is more than BMW charge for service and he is working from a shed at the back of his house.

There will be a wire connected somewhere to the throttle linkage on the engine which shorts the circuit to stop the engine. Check that is properly connected.

Mike

[newshound]

Unless the throttle is intended to shut off all air in the "stop" position, as on my powered barrow. So could be an air leak or badly adjusted throttle cable.

[Tim+]

I think "electronic gubbins" hints at an electrical cut-off mechanism.

Tim

[Brian Gaff]

Or just fit a kill switch in the spark plug lead of course. However sounds a bit dodgy if it cannot be stopped in the normal way. Brian

[www.GymRatZ.co.uk]

Ha.... I was just abut to start a reply with the same line.

:)

[Theo Markettos]

It's not a good idea to interrupt the HT with a switch, because it'll just arc over the switch contacts - that's what a spark plug is after all.

Shorting it with a big piece of metal sounds like a good suggestion. Or you can interrupt it but you need a big enough air gap to avoid arcing. Shorting is better because there's no chance of it inadvertently finding a route to ground through you.

Theo

[Johny B Good]

Absolutely true! It's worth remembering that the voltage required to jump a 25 thou gap in a compressed atmosphere of air/fuel mixture will be quite capable of jumping a half inch or longer gap in air at

1000mBar (somewhere around the 20 to 40 KV mark).

That's why such stop mechanisms were used. Simple and reasonably safe against getting bitten by the EHT leakage. Not only that, it avoids the risk of HT coil winding insulation breakdown due to removal of the voltage limiting arc gap of the plug electrodes if you were to introduce an old fashioned DC tumbler switch[1] with its 15 mm or more contact gap over a porcelain substrate in series (earthing the metal cover of such switch for personal safety).

[1] With DC supplies, there's no convenient zero current crossings 100 or 120 times a second to extinguish the arc which permits the use of modern day ac mains light switches with their mere 2 or 3mm gap. DC lighting switches needed to seperate the contacts by a very much wider gap in order to extinguish the arc on switch off.