1974 commando dead as a duck, need help!

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toobeesa

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Dec 3, 2014
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Hello my friends,i have a1974 Norton 850 roadster.I bought it at an auction,not running.I cleaned the carbs,cleaned and set the points,set the timing with a timing light,and got it running.It has been starting and running good.A few times it just quit running,like I had turned the key off.I knew about the fuse on the battery side, so that was the first thing to look at,I took the fuse out, and it was fine,put it back in, and everything came back on.This happened 3 times,till today it went dead and would not come back to life.This bike has 13 k miles,and is in almost perfect condition,clean as a whistle,so it should be a simple fix,i just dont know were to start in the wiring or is it a lucas part gone bad? Any help would be a god send,thanks
 
Sounds like a poor connection to me. Either a loose connection, or, at least as likely, a broken wire into a connection.

Good news here is that if this is the cause, its a zero cost solution.

Bad news here is there aren't any shortcuts, you'll have to go through one by one.

But at least you'll get to know your way around the wiring!
 
At least while the bike is not working then the fault should be easier to find and cure. I once had problems that turned out to be the fuse it's self have a badly soldered joint between the end cap an the fuse wire that gave erratic contact.
 
Its 100 plus here in kansas so i have time to check the wiring out,i think thats the problem.
 
First place to look at is the fuse holder itself, they get curosion, or the wires break and is easy to replace, if that don't fix it them just go through all the wiring and check as you go, doen't sound like a lucas part faiure to me more a wiring conection or lose wire, could even be the ignition switch who knows till you get into it, do you have a multie meter as that will help you to trouble shoot your wiring, have the power turned on and shake the wiring as you go, could even be a dirty or coroded earth wire some where.

Ashley
 
I would also suggest checking the ignition switch or bypassing it. It happened on my mkiii and my previous commando, a 72 Interstate
 
Tracing down a wiring fault like this doesn't have to be as daunting as you might think. Since your fuse isn't blowing, it's a good bet it's not a ground fault. Just isolate the key components of the ignition system (pick up plate, kill switch, ignition switch etc...) and use your volt meter to check the resistance along each circuit. Jiggle the wires while you're doing this.

Rule of thumb is that the fault will usually be in the last circuit you check...
 
ashman said:
First place to look at is the fuse holder itself, they get curosion, or the wires break and is easy to replace, if that don't fix it them just go through all the wiring and check as you go, doen't sound like a lucas part faiure to me more a wiring conection or lose wire, could even be the ignition switch who knows till you get into it, do you have a multie meter as that will help you to trouble shoot your wiring, have the power turned on and shake the wiring as you go, could even be a dirty or coroded earth wire some where.

Ashley
Click to expand...
Thank you,I never think of corosion and loose conections,I do have a meter.
 
acadian said:
Tracing down a wiring fault like this doesn't have to be as daunting as you might think. Since your fuse isn't blowing, it's a good bet it's not a ground fault. Just isolate the key components of the ignition system (pick up plate, kill switch, ignition switch etc...) and use your volt meter to check the resistance along each circuit. Jiggle the wires while you're doing this.

Rule of thumb is that the fault will usually be in the last circuit you check...
Click to expand...
You may be right, that kill button wire drove me nuts on an old commando years ago,thanks for reminding me.
 
Change the fuse. It may look okay but the solder between the link could be cracked or corroded.
Also check the two ends in the fuse holder to ensure the wire is secure in the contacts.
If the fuse is blowing disconnect the Zenner diode if it is still used.
 
Remember its 40 years old connectors get old, loose or coroded, kill switches get corosion as well, wiring goes hard from the weather over the years of cold to hot as we don't know where your from, so wheather the bike has been kept out in the cold or what it all plays a part with wiring, wiring gets brittle and breaks just moving it from old age, moisture plays a big part with wiring as well, so hope its just something simple and good luck with it.

Ashley
 
40 year old switches tend to have high resistance when they get dirty. I'd go through anything that is in the ignition circuit that may cause the problem, that includes any harness connectors. A resistance check may not be good enough, you may need to put a load on the circuit and measure voltages as you go along from point to point and it may be good today and bad tomorrow. Clean and use De-ox on all the connectors and switches, just to start with. You don't want to be passing that dump truck when the ignition switch decides it's had enough.
 
Hi guys,

+1 about by-passing the ignition switch and feeding the ignition directly from the battery with a very simple and reliable ON-OFF switch.

I've been bothered for months with sudden ignition cut-offs at different rpm's and sorted it just today with that "by-pass" solution.

But it won't work if your problems are due to other ignition components' failure (eg : the condenser if it stops when hot and works when cold).

Hope it helps.
 
I'd try disconnecting the capacitor (the big blue thing mounted in a spring). I run my bike without one after it decided to randomly blow up and stopped the bike dead. Just tape up the wires, don't join them together.
 
laurentdom said:
Hi guys,

+1 about by-passing the ignition switch and feeding the ignition directly from the battery with a very simple and reliable ON-OFF switch.

I've been bothered for months with sudden ignition cut-offs at different rpm's and sorted it just today with that "by-pass" solution.

But it won't work if your problems are due to other ignition components' failure (eg : the condenser if it stops when hot and works when cold).

Hope it helps.
Click to expand...


Those nasty little condensers, I have been caught out with one of them but the bike is not starting when condenser go they will start the bike up but once they get hot thats when they will play up, mine was causing my motor to misfire, but when I put a Boyar in it in the late 70s it gets rid of all that (condensers, bellas resitor), I have also been caught out with a faulty ignition switch, I now only run a toggle switch to stop my motor as now I run a Joe Hunt maggie and only have minamal wiring on my Norton now.
 
A key troubleshooting step is to determine if all electrics are dead, or is it just the ignition. If everything is dead, you need to start at the battery and work through the ignition switch. If it's just ignition, then check the harness bullet connector junction block (under the tank) and the kill switch itself. The kill switch on my 74 went intermittent within a couple years (I'm original owner).

The workshop manual with schematics are available online.
 
acadian said:
Rule of thumb is that the fault will usually be in the last circuit you check...
Click to expand...

Of course it will, as you'll stop checking once you find it.... 8)
 
Excellent advice from Maylar. While you are at it, once you know what wires are for what, set yourself up with an emergency hot wire procedure that powers up the ignition directly from the battery. I have a wire hooked to the battery ready to just plug in to feed the ignition. I do not use the kill switch circuit either. I did have a Norton once that had the most devious electric fault ever. It would just die sometimes without warning. I finally found that the resistor had a broken wire right where it connected to one of the lugs. Current passed the crack most of the time but when you least expected or wanted it, the bloody thing just died. If the Zener goes direct closed circuit, that is in the wide open current flow mode, the main fuse will pop instantaneously. Your only hope of getting home is to disconnect the main battery positive lead and run a jumper wire to the ignition off the positive post. Been there done that. Never been stranded on my Nortons.

PS I am 67 years old today and have been enjoying my Nortons for some 40 years.
 
aceaceca said:
Excellent advice from Maylar. While you are at it, once you know what wires are for what, set yourself up with an emergency hot wire procedure that powers up the ignition directly from the battery. I have a wire hooked to the battery ready to just plug in to feed the ignition. I do not use the kill switch circuit either. I did have a Norton once that had the most devious electric fault ever. It would just die sometimes without warning. I finally found that the resistor had a broken wire right where it connected to one of the lugs. Current passed the crack most of the time but when you least expected or wanted it, the bloody thing just died. If the Zener goes direct closed circuit, that is in the wide open current flow mode, the main fuse will pop instantaneously. Your only hope of getting home is to disconnect the main battery positive lead and run a jumper wire to the ignition off the positive post. Been there done that. Never been stranded on my Nortons.

PS I am 67 years old today and have been enjoying my Nortons for some 40 years.
Click to expand...


Happy Birthday and hope you are still riding when you turn 100.

Ashley
 
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