Last gasp when turning key off.

What it does, sometimes. Usually if I am riding for a while.
When I stop and park the bike. I kill it with the kill switch. Turn off the headlight. Turn the petcock off.
Reach down and turn the key to turn the bike off and remove the key. When I turn it, I get not quite a pop, more like a puff, like it is burning a last bit of gas.

Not sure what it is. It does not do it all the time. Maybe once every 10-15 shutdowns.

It seems as if there is some unburned gas and turning the key is creating a spark to burn it.

Any ideas? Anything to be worried about?

drones76 said:

What it does, sometimes. Usually if I am riding for a while.
When I stop and park the bike. I kill it with the kill switch. Turn off the headlight. Turn the petcock off.
Reach down and turn the key to turn the bike off and remove the key. When I turn it, I get not quite a pop, more like a puff, like it is burning a last bit of gas.

Not sure what it is. It does not do it all the time. Maybe once every 10-15 shutdowns.

It seems as if there is some unburned gas and turning the key is creating a spark to burn it.

Click to expand...

Some electronic ignitions do that.

To check, remove the spark plugs, fit them to the caps, lay the plugs on the cylinder head and see if the plugs spark when you operate the ignition key on-off. If so, then that puffing sound you occasionally hear is probably unburnt mixture igniting in one of the cylinders from the spark generated when the ignition is switched off.

Yes ,my early model Boyer ign. does the same (firing) upon on-off switchage to a pulled plug . Prefer it actually over later ones as it's easier to verify good sparkage as the new models are not definate to fire upon observation and subsequent troubleshooting. Sometimes they spark ,sometimes not so I'm appreciating this with the early model.

Yep some electro brain boxes give a spark when turning on or turning off and can be a danger is done while in gear and bike is on a slope on side stand or fiddling with something near spokes or chain and ya bump a loose connection in ignition circuit - it can fire enough to move parts enough to hurt you. On the other hand I and a handful of others have shut down gone in and come out fast enough that when we turned key on it fired up at idle. This sparking w/o engine turning is a good thing to help diagnosis bad conduction by leaving key on then jiggle stuff until a spark then narrow on down to fixed.

My old `73 Mopar came factory equipped with an E-ignition, it will like-wise fire off under similar circumstances.

My 850 fired up twice by just turning the key on and its not a elec.start (74) with the old boyer ignition, the first time it did it I was setting the timimg and my mate was sitting down near the kick starter and I was on the timing mark side of the Norton, when I turned the key on the bike fired up and was idling at the right speed, after a while my mate just looked at me and asked how I did that when I wasn't even near the kick starter, I just laughted and said magic and left it at that, had him stuffed, that was over 25 years ago and I never did tell him how it happened, my mate got killed in a motorcycle crash about 1 year later, just reading this Last gasp just made me remember my best mate.

Ashley

Thanks for the responses. For the record, I have a Pazon ignition. Glad it is 'normal' and one less thing to worry about.

I used to have a Triton with an 8 valve Weslake head on a T120 engine and Boyer ignition, it had no key just the kill switch (which was part of the twistgrip cluster from a Suzuki ) the bike looked a bit ratty and would draw some smirks and unkind comments from the local lads on their 250 Yamaha's and Suzuki's.
I had got this technique down to a fine art, with a warm engine set just over TDC it would fire up with a flick of the switch.
On this particular day the bike was parked up against the wall of the bank(No Main or side stand)and I came out to find the young "Local crew" standing over it, the comments started about it being a "shitheap" and "Old Brit junk" so I smiled, prepped the bike, got on flicked the switch and it fired up straight away.
I wish I'd had a camera, the look on their faces will be etched in my mind forever.