Won't start...possibly electrical

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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GeoffR
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Joined: Wed May 24, 2017 1:37 pm
Location: GLOS UK

Won't start...possibly electrical

Post by GeoffR »

Hi

My 1961 G12 won't start. She's usually pretty reliable but when I switch the ignition on the ammeter doesn't register at all so I thought I had a dead battery. But I have charged it up and checked it with a voltmeter which shows just over 6 volts. I have also checked the fuse on the battery live wire and that is ok as well.

As you can tell, electrickery is not my strong point so I'm looking for some pointers as to what to look for. Some one said that the battery may show 6 volts but needs to be under load to be checked properly, but I don't think its the battery.

Any helpful suggestions would be welcome.

Thanks
Geoff
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clive
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Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Won't start...possibly electrical

Post by clive »

You need to approach it methodically. I would start by checking the battery will light the headlight which will check it can take a load. You could do this by just trying the headlight switch but you are checking more than one thing at once if it does not light up. In that event I would take the bulb out and try it directly linked to the battery. Do you have a multimeter? If not I would invest in one and you can then check the continuity of wires one by one. I would look at your battery earth point, clean it up and hope that sorts it. Failure of the ammeter is another possibility as they can go open circuit. If the headlight is working when you switch it on you may have a problem with the coil or the circuitry to it (out of my knowledge I am afraid as all my bikes have magnetos) .
do some more test and come back with the results
clive
if it ain't broke don't fix
SPRIDDLER
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Location: WEST SUSSEX UK

Re: Won't start...possibly electrical

Post by SPRIDDLER »

GeoffR wrote: Mon Jun 07, 2021 12:49 pm when I switch the ignition on the ammeter doesn't register at all
Just to clarify ref the non starting: Is there a spark at the plugs?

I don't think you'll see a discharge when you turn the ignition on unless the c/b points just happen to be closed. When you turn the engine over the ammeter should deflect every time the points close.

With the headlight on you should see a discharge on the ammeter.
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Which taken at the flood............'
g80csp11
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Joined: Mon Jan 01, 1990 12:00 am
Location: WEST SUSSEX UK

Re: Won't start...possibly electrical

Post by g80csp11 »

lots of things you can check for starters , generally coil / distributor system are very reliable provided they have power

If you remove the spark plug , and turn on ignition then slowly turn over the engine the ammeter with show a discharge at some point while its charging the coil and then return to center (zero) as you continue to turn over engine . if this is not the case then options are:

- Ammeter has failed ( check that when you turn on lights it moves as normal)
- points not opening (as Clive says , clean , reset gap)
- no voltage supply to coil ( one side is earthed via points , the other is power )
- dead battery (if you turn lights on does ammeter show discharge and do they actually come on )
- failed coil
- Distributor not turning
- HT lead from coil to distributor as come off
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