I've killed my spark and fuel supply - how on earth...?

[nimrod650]

Yes , there is a kill button, opposite the horn button on the dip switch. I should have thought of that. Have to go out in four minutes, but this evening will give that a good wiggle. I certainly used it to stop engine when I came home on Thursday, which is the last time I saw a spark. That would be a wonderfully simple and logical solution - and somewhat easier than stripping down a mag to replace condenser. The points do open and close fuller as far as I can tell with a feeler gauge, and was running fine before, so I don't think anything has jumped or slipped. Is there a quick way to disable kill switch - can I simply disconnect a wire?

i run the mag wire to a lucas fog light switch under seat also acts as anti theft device when parked up

[CrispinA10]

OK, really simple but stupid question - where does the flamin' cutout switch wire go into the magneto? The only wire I can see is what I assumed was the high tension cable, which goes into the mag cap in the centre and is secured with a serrated washer, plain washer and nut. Surely that's not the cut-out wire? The Haynes manual suggests that it is, Is it really? And if it is, how on earth is the mag wired in to provide a spark - I can't see how that could work. But I do confess to being pee-poor at electrics. Preferred iambic pentameter to resistance and multimeters at school. Still baffled by the twilight world of Joe Lucas, Prince of Darkness.

[Billybream]

That's the cut out wire, the ht cable or spark plug leads go into pick up carriers either side of the magneto. These must be connected to provide power to spark plugs.

[Greybeard]

My knowledge, which I obtained from the book Magneto's for Dummies, (no such book) says that the wire that's connected to the centre, or side of the end cap just shorts the mag to earth via a push button kill switch originally fitted on the handlebars, (and/or an after market toggle/keyed switch, usually hidden somewhere to provide some kind of engine immobiliser). If that single wire is connected to the machines earth the magneto stops working. As long as the mag body is properly earthed it needs no other power source or external connection apart from the HT leads going to the plugs.

In the old days, anyone who knew anything about motorcycles would know that popping off the end cap or cutting the kill wire was enough to counter the simple switch idea. These days I comfort myself by thinking that there cannot be many bike thieves who know these tricks.

[CrispinA10]

If anyone planned nicking my Beezer they would have a hell of a job pushing it up two miles up the lane and onto the main road - it isn't going anywhere at the moment. Disconnected the mag cap centre wire and despite my best hopes, nothing. Still no spark. Didn't touch anything other than using abrasive strip (wife's nail thingy) to clean up points so still at a loss as to why no spark. Points are now spotless, perfectly gapped but still nothing. Unfortunately have to work tomorrow so no chance to delve deeper. Argggh.
Still love it to pieces though...

[nimrod650]

My knowledge, which I obtained from the book Magneto's for Dummies, (no such book) says that the wire that's connected to the centre, or side of the end cap just shorts the mag to earth via a push button kill switch originally fitted on the handlebars, (and/or an after market toggle/keyed switch, usually hidden somewhere to provide some kind of engine immobiliser). If that single wire is connected to the machines earth the magneto stops working. As long as the mag body is properly earthed it needs no other power source or external connection apart from the HT leads going to the plugs.

In the old days, anyone who knew anything about motorcycles would know that popping off the end cap or cutting the kill wire was enough to counter the simple switch idea. These days I comfort myself by thinking that there cannot be many bike thieves who know these tricks[quote they just chuck it into a van anwayauthor=Greybeard link=topic=10877.msg81637#msg81637 date=1468697688]
My knowledge, which I obtained from the book Magneto's for Dummies, (no such book) says that the wire that's connected to the centre, or side of the end cap just shorts the mag to earth via a push button kill switch originally fitted on the handlebars, (and/or an after market toggle/keyed switch, usually hidden somewhere to provide some kind of engine immobiliser). If that single wire is connected to the machines earth the magneto stops working. As long as the mag body is properly earthed it needs no other power source or external connection apart from the HT leads going to the plugs.

In the old days, anyone who knew anything about motorcycles would know that popping off the end cap or cutting the kill wire was enough to counter the simple switch idea. These days I comfort myself by thinking that there cannot be many bike thieves who know these tricks.

[/quote]

[morris]

how on earth is the mag wired in to provide a spark - I can't see how that could work. But I do confess to being pee-poor at electrics. Preferred iambic pentameter to resistance and multimeters at school. Still baffled by the twilight world of Joe Lucas, Prince of Darkness.

Very pretty looking machine you got there Crispin 

Everyone calls a K2F a magneto but in the strict sense of the word, a magneto is just a device that makes electricity and does just that.
The K2F on our bikes contains a magneto (the square shaped part opposite to the points side) to generate power for the spark.
That's why you don't need a battery or other external power source. The magneto generates low tension power, which is transformed to high tension by the opening and closing action of the points, and it's this high tension you need to generate a spark.
This high tension is distributed to the spark plugs by means of the slipring which is driven by the magneto shaft.
The slipring is made out of a non conducting material and has a bronze insert that passes by the pick up carbon brushes and thus sends the high tension to the correct plug.
The condenser is just there to prevent the points from arcing, as this arcing would otherwise wear them out fairly quickly.

It's known that bad quality pickup brushes can leave a trace of carbon all around the slipring so the whole circumference of the slipring becomes conductive. The spark will then follow any path and end up god knows where...
Remove the rear pick up brush, and have a peek in the hole. If there's carbon on the ring it will be clearly visible.

[CrispinA10]

Unfortunately no need to be able to whip off the plug caps to stop the motor - there is still no spark with the kill switch cable removed. Off outside to have another fiddle before I have to go to work.

[mugwump]

This thread is like the episode of  Hancock's half hour show ( Brits only will be familiar with this show) 'The last page'. Hancock's frustration at the last page missing from a borrowed book.
Is there a happy ending to this story CrispiA10 ? 

[CrispinA10]

Apologies for the delay - arrived home from holiday six minutes ago. Hoping the pixies have been in the shed and sorted it while we've been away, but they probably haven't. Full day off tomorrow before returning to work so will be trying again and will report.
Thanks for all the help so far - really looking forward to rekindling that spark in my relationship with my BSA...

[CrispinA10]

Taken the magneto cover off and had a good long stare and fiddle again. I am reluctant to start taking things apart on the grounds that it was sparking fine until I cleaned the points, and that anything else I do could make the problem more difficult to trace. I don't think I took too much off with the abrasive paper - the gap seems to be 0.012 -0.015 depending on the exact definition of slide fit. I have taken off the cut-out wire just in case that is having an effect, although it doesn't appear to be the issue. Still no spark. I have taken the plug caps (unsurpressed) off and am holding the HT lead close to the head hoping for a spark - is there a better way? I know that mag systems don't need a battery. The reason I mentioned a charge earlier was that with my Enfield (which has a different points system) it is easy to induce a spark between the faces by separating them with a thin wooden probe, thus checking that all is well. Can't do that with cam ring set-up of course.
I noted the advice to "remove the rear pick up brush, and have a peek in the hole. If there's carbon on the ring it will be clearly visible" Looking at my Haynes manual I'm not sure exactly what the rear pick up brush is. Is it what is marked High Tension Pick-up? Or is it the Earthing Brush? I'll have a look, but if there was a carbon issue, surely it would have been apparent before. Incidentally, my mag doesn't look the same as the one on page 84 of Haynes, Fig 5.1 The Magneto Components. I did include  picture of the points end of mine and was told it was the later type. The unit was professionally reconditioned for the previous owner (and builder) and has so far done about 800 miles.

[Triton Thrasher]

The spark should be capable of jumping 1/4" from the lead to the cylinder head.

The slip ring, which can get coated in carbon, is sort of visible when a high tension pickup is removed.  Check that the brushes in the HT pickups have not stuck out too far and been sitting sideways against the slip ring.

Clean the slip ring with petrol on a rag, while turning the engine over.  Remove the points, or short-cicuit the kill switch lead, to avoid shocks.

[chaterlea25]

Hi,
BY any chance did you remove the complete points rotor?
On replacing it are you sure the rotor key is located properly in the armature?

Another possibility since the mag has only done 800miles since rebuild and the points have pitted is that the condenser has failed
There were and are a lot of unsuitable condensers being fitted
Failures of condensers have similar symptoms to yours

John

[CrispinA10]

No, I didn't remove anything - just a light clean of the faces.
Thought I had found something just now. Following the advice to check the HT pick-ups, did so and found that one in particular was a bit loose. Checked the carbon springy things and they look OK (although not sure exactly what I am looking for). Refitted them and tried to squeeze the retainer strips in a bit to create a tighter fit, turned it over without plugs in and...nothing. If I hold one of the bare leads and kick it over, there is no hint of a shock. And I know what an HT shock feels like after an unfortunate incident with a James Captain when I was about 14. Quite a jolt.
Just how tight should those pick-ups be held in? Not too tight I assume or the carbon brush would wear too quickly.
Seems unlikely that the condenser would pack up completely at just the moment I cleaned the points, but wouldn't I still get a weak spark?
Another possibility: How critical is the tightening of the bezelled ring that holds the black Bakelite end cap in? There is a little brass triangular marker which sits in one of the grooves, but no indication of which one it should sit in. I took it off and put it back fine the first time, but could this be an issue? I have it finger tight at present.
Off to wipe the slip ring (which I assume is the thing I can feeling turning beneath the pick-ups) with petrol as advised.

[chaterlea25]

Hi Crispin,
At this point I think you need to recruit some help from an experienced person or workshop 
Are there any forum members in your locality who may be able to help?
These magnetos are fitted to quite a few different makes of bikes so not necessarily a BSA owner???

John