To Kill or not to Kill….

This was my take on it. Using a relay to switch off the power feed from the ignition switch.

Engine kill switch for Boyer/Wassel EI | Norton Owners Club

I am glad I did it for safety and also to kill the engine when walking it onto a trailer.

Eddie

Warming up the old Manx, throttle stuck 1/3 open. Flipping the kill switch saved a lot of money and work. So I'm fitting kill switches on my bikes. Though not done it yet on the ones with decomp lever.

Prefer on/off switches to push to kill switches. On battery ignitions they just open supply to the ignition circuit. On magnetos end caps with cut-out.

Also on some of the bikes don't have idle. Kills engine when letting throttle go. Habit since my speedway racing youth.

I removed the kill switch on my Mk3 850 when I changed the master cylinder. It was a nuisance as it was so easy to knock off, especially with a tank bag and I'm pretty sure that I'd never have found it in a panic. The Mk3 though does have the ignition key up on the console which is where I think of to turn it off.

I once owned a Benelli 2-stroke twin which had a habit of dieseling. That was strange, pull the plug caps off and it kept going. Blocking the silencers was the only answer.

I’m disappointed to learn your mk3 isn’t standard, shocked even 

... ever since I let my brother have a ride on my Triumph Tiger 955i. He returned it after an hour with the exhaust ticking and the tyres all frazzled. Next day when I went to start it the engine would turn over but wouldn't fire. After half an hour stripping bits of plastic off looking for a fault my eyes alighted on the kill switch. Sure enough he'd used it to stop the engine - something I've never done.

So I'd leave it off. You can always turn the ignition key off.

.. in this garage, on my Moto Guzzi...shock horror (didn't leak oil!!!) filled up with petrol, paid the dues (sensible money) giger gagger on the starter ..nothing. A young lady motorcyclist who just happened to be passing, wandered up pointed to the handlebar ignition kill button-OFF! You feel so foolish. I then though of ways to stop the starter circuit working when the kill was off, saves running the battery out!

Be aware on relays in this usage, makes sure you fail SAFE. Talk to me if you have any fancy circuits, I can help.

Mikael's comment about the Manx throttle sticking open reminds me...the magneto on the Singles has no convenient earth cutout unless it is modified. So we are left with the decompressor (unless the engine can be safely stalled).  I'm not keen on using the decompressor from say 3000rpm... are there good reasons why not?  Might the exhaust valve hit the piston? And impact between cam lobe and follower might be severe?  How many owners check piston to valve clearances on OHV and OHC engines with decompressor engaged?

I feel the need for a kill switch...

I had a similar experience when I went to the Red Marley hill climb on the same Tiger. I left it parked in gear on the sloping muddy field which acted as a car park. After a great day watching some fantastic riding I returned to the bike, swung a leg over, pulled in the clutch and thumbed the starter. The engine turned over merrily but didn't burst into life. A kindly passer by pointed out that it was designed to work like that if the prop stand was down and it was in gear. Again, why not disable both starter and ignition?

I'm not keen on using the decompressor from say 3000rpm... are there good reasons why not?  Might the exhaust valve hit the piston? 

The instructons I work to are from BSA, they say to have the exhaust valve lifting just as the lever is nearly fully pulled in. So the exhaust valve is only lifted a few thou which is all that's needed. No chance of the piston hitting the piston or the cam clearance being so large there are extra forces involved. Even if not which is preferable, a bent exhaust valve or a destroyed engine. 

Makes sense...ta John.  It doesn't apply to the SV but Franks etc don't discuss it in the Norton books as far as I know.

can be hard to arrange, if the mag was not designed for it.  I once made one for a magdyno, using a plastic spray can cap and an earth brush.  I made the mistake of leaving it on the magneto when I sent it off for a rebuild, and did not get it back.  At least the mag gives a spark now

....subject of this post, I sell a magneto kill switch. This is only usable when there is a built in Mag Kill as in K2F or even K1F. It earths the magneto and opens the battery line so that lights, stop lights cannot be left on.   aoservices.co.uk