Commando runs for 10 seconds and quits

This was a topic addressed in prior threads and I wanted to tell you my experience with it so you can avoid the same issues. I had this problem re-occur no matter what I did. My '74 850 just quit on me. After a lot of tests, I was sure it was the very old electronic ignition so I changed it. Same problem...10 seconds and she dies. The spark was weak and intermittent. Changed the ignition switch, pulled the carb countless times, tried my old carb, same problem. Bought a new carb as it was time anyway. Fresh plugs, fresh gas, checked the loom for shorts. New battery. Nope. Still a weak, intermittent spark. Suspected a faulty CDI. Ordered another new one! (Weeks have now gone by.) Made no difference. Finally, on the suggestion of a friend, ran a wire directly from the battery to the CDI and got a better reading. FINALLY FOUND THE PROBLEM in the kill switch. The ignition wire to the CDI routes through the kill switch. Although the switch itself tested okay and had no loose wires, it was creating enough resistance to draw off the current to the CDI. As soon as it was by-passed, I got the spark like never before (damn well should with all the money and time!) and she is back to first-kick and running like a top. As I say, I hope this is helpful to someone out there. In a way, it is one more proof to stick first with the simple diagnostics no matter how pedestrian they may seem....but it is also true that if we could solve everything with hindsight.....well.....we can't. At least I am back on the road. Hope you are too.

This is the great forum! sharing Problems..and better still, how they where fixed! Great post 10/10 This makes a change from the constant rubbish. :!:

Merci, QB. This has been mentioned, often overlooked trouble spot. Mine flakes on me intermittently now too.

Getting a reply like that from you Mr. Bould is appreciated. Fitting the Landsdowne kit was one of the most significant upgrades I have ever done to a bike.

Glad you found your trouble. I went through the same scenario last year, it turned out to be a bad ground to the ignition circuit. The multi-connector female plugs used in the original harness seem to be prone to splitting causing intermittent loss of ground. In my case it was only when the bike was running with things shaking around like they do. Enough to drive a person to drink sometimes!

Shucks Bob! Thank you. So sweet motor and handling! Enjoy.

Quebec Bob said:

Getting a reply like that from you Mr. Bould is appreciated. Fitting the Landsdowne kit was one of the most significant upgrades I have ever done to a bike.

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Quebec Bob said:

Getting a reply like that from you Mr. Bould is appreciated. Fitting the Landsdowne kit was one of the most significant upgrades I have ever done to a bike.

Click to expand...

CDI ??? Never heard of a british bike ignition standard product that was a Capacitive Discharge Ignition. It should however be a fairly low current draw since an analog boyer or Rita should be much higher surge current and then suffer even more under a resistive kill switch.
But a bad lucas kill switch is not new. Glad you found the problem.
Please advise. CDI....

why would a 74 850 have a cutout/kill switch? LAB?

Great post. So many problems discussed here go on and on and no resolution is reported. I, like many here, have worked on machinery my whole life and yet it seems I encounter problems that stump me on many occasions. A good one on me that relates to your problem was on a stock point driven Commando. It would just die all of a sudden with no warning. Turned out it was the resistor wire split in two near the lug. Made contact most of the time but not always. It was also difficult to see. On the same bike I found in the main harness, with the 6 or so connectors all in on, the ignition wire had melted insulation.
Probably caused by leaving the key on with the points closed. Then there are those Boyer connections that everyone should have resolved by now. Each one got me at different times. And the list goes on and on.Like any machine, once the inherent problems are rectified, all is well. My Commando has never failed to bring me home and nothing has ever fallen off it, including me thank goodness. Once a float bowl tried to fall off and drenched my pant leg in fuel. I got her home by throttling the fuel petcock. Problem solved. When my Zener failed closed and blew the fuse I had to hot wire to the ignition to keep going. I recommended to all that you should have a pigtail on your battery and knowledge of the ignition wire needed to be powered up so you can keep going in an electrical emergency. You can drive all day on battery power alone. A good forum topic would be rider reports on problem or fault encountered and solution used or found. All posting must have confirmed resolutions. Not ones that say, I tried this, then this, and that, but the weather was bad so I could not try it out. Then you never hear from them again. End of story.

dynodave said:

CDI ??? Never heard of a british bike ignition standard product that was a Capacitive Discharge Ignition

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Many people wouldn't know what the difference was between a CDI and any other type of electronic ignition, so to some, it's a 'CDI', regardless, even though it might not be entirely accurate.

pete.v said:

why would a 74 850 have a cutout/kill switch? LAB?

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But, why wouldn't it? :?
'71-on models had 'kill' switches as standard, either a push button or toggle switch (850 MkIII).

Quebec Bob said:

Finally, on the suggestion of a friend, ran a wire directly from the battery to the CDI and got a better reading. FINALLY FOUND THE PROBLEM in the kill switch. The ignition wire to the CDI routes through the kill switch.

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Why can't the power supply be run directly from the battery via a relay controlled by the ignition and kill switch ?

This is exactly why one needs to measure voltages at the end points during use from a good ground point, not check circuits with an ohmmeter. This would have shown a large voltage drop across the kill switch, undoubtedly. I've had the same problem with my ignition switch, but it wasn't 10 seconds, it just didn't work.

L.A.B. said:

[

pete.v said:

why would a 74 850 have a cutout/kill switch? LAB?

Click to expand...

But, why wouldn't it? :?
'71-on models had 'kill' switches as standard, either a push button or toggle switch (850 MkIII).

Click to expand...

OK! I thought it was just a safety feature needed for E-starts. I see little evidence of them in schematic other than the MKIII's.

Commando runs for 10 seconds and quits

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Think its trying to get you to enter a drag Meeting . ! Ten Seconds should do it . :mrgreen:

pete.v said:

L.A.B. said:

[

pete.v said:

why would a 74 850 have a cutout/kill switch? LAB?

Click to expand...

But, why wouldn't it? :?
'71-on models had 'kill' switches as standard, either a push button or toggle switch (850 MkIII).

Click to expand...

OK! I thought it was just a safety feature needed for E-starts. I see little evidence of them in schematic other than the MKIII's.

Click to expand...

The switch (and its wiring) is there on all the usual '71- wiring diagrams.

I kind of think that a kill switch is a safety requirement. ??

And once having had a throttle stuck open (unravelled throttle cable), I rather know why.
Much better than fumbling around looking for the ignition key, while negotiating obstacles at speed.
Or pulling the clutch in while fumbling around and steering....

The kill switch on these 71 on models has been a bit of an Achiles Heel as the bikes and their wiring gets older. I think it is a good idea to run a kill switch and I simply use the original kill switch wiring to trigger an A-B switching relay under the tank near the coils. The relay's default position is; ignition power feed to the B circuit when the ignition key is on then switching to open circuit when using the kill switch to break the earth. If any voltage drop is experienced between the two wires of the kill switch this is non-critical for the purposes of switching a relay on or off, as you are simply providing an earth to the relay. If you are using a kill switch that earths to the handlebars, then simply wire this to the other side of the relay using the A circuit to feed the ignition and the B circuit as the open circuit when the kill switch earths through the handlebars. I believe there is a chance of damaging an electronic ignition if you simply earth it through the bars to stop the bike without using a relay. This could give a whole new meaning to the term 'Kill Switch'.

The Norton kill switch is a killer diller as one must keep constant finger pressure on it long enough the rpms slow to stalling speed which in some of my case was impossible to do yet I'd been able to toggle it for almost a second till brashed brain/broken neck and major lower limb joints that put L foot in midback and R boot seam trapped under cracked off foot peg remains on side of THE Gravel embankment so my head lower by couple yards from the bent bars putting the kill switch out about axle distance from expected at wonderful slow idle while gasoline drooled past soaked pants enlarging puddle I was lain low in and couldn't reach key a yard+ beyond any range of motion I could attempt between time my heart wasn't just vibrating in fiberation no pumping with death gurgles of mangled deer near my head just like my sounds & involuntary nerve death twitches > to say don't kid yourself with the Norton switch use but to pull up and cut off in gear not to roll away from gate to work while bike balanced on a fence post -> to put a definitive one action ON-OFF! or a jerk cord kill like the over powered door skin veneer/wing fabric lightweight hydroplanes going sideways and steering into the decreasing radius bend in canal between lakes through the wake of a displacement boat on top the wind created chop funneled though the bridge channel over head. Just saying for the any with brains left to consider future fate they might face if still stupid enough to enjoy these sort of events repeated who knows how many times among us all.