AJS & Matchless Owners Club

Hi

My 61 G3 has not run since 1975 and I'm in the final stages of restoring it. I have had to partially re-wire it due to the original Lucas 63SA switches being beyond repair and have done this in accordance with the 1964 singles wiring diagram utilising 88SA switches, I'm pretty sure I have all in order but I cannot get a spark at the plug.

I have:
A new battery which is providing 6.3 volts at the coil and CB - the coil checks out with 2 Ohms across the LT winding and 4.19 K Ohms across the HT winding, (no leakage to case from either).
Brand new HT lead, fittings, plug cap and spark plug, (gapped to 0.020") - continuity confirmed.
Points are original but cleaned and confirmed to be operating correctly both mechanically and electrically.
Capacitor is original - could a dodgy capacitor cause issues at the plug? I thought it was there to prevent the points from arcing.

I have tried:
Turning the engine by hand, (via the kick start - the bike is on a lift presently), in both normal and emergency - no spark observed.
Manually opening and closing the points in both normal and emergency - no spark observed.
Connecting the battery directly to the coil -ve, cycling the positive lead to the coil at about one second intervals - I occasionally see a very weak spark.

I'm stumped for now

I am wondering if my plug cap could be a contender for the cause - I have fitted a suppressed NGK LB05F one which has a 5K Ohm resistance, could this be the cause of my problem?

Can anyone suggest where else I could look for a solution please?

Regards Mick

I'd change the old condenser. It's cheap and you don't need to alter any settings.

Also why not take off the plug cap and see if it sparks against the head? Definately get another condenser as Janet said, but don't throw the old one away, and try several. Try to get an old stock Lucas. A lot of the new pattern ones are rubbish.
Dave

The suppressor plug gap won't affect spark performance - 5kohms is negligible at spark voltages...
It sounds like your coil isn't working properly. You should get decent spark just by wiring it up to the battery and pulsing the feed to it (as you've done).
If the coil is original, the insulation may be degraded and it could be flashing over internally.

Throw away the condenser and fit a BrightSpark equivalent that doesn't rely on aluminised foil. I had a lot of trouble with conventional condensors but the BrightSpark printed circuit has been good.

But it is a good idea to eliminate the plug and plug cap and check the spark from the end of the HT lead to the head.

So long as it's not my head.

Johnny B

Hi

Thanks all for the suggestions, I will try replacing the coil and if that doesn't work go for the capacitor. This is following further diagnosis of repeating my previous tests with another lead and plug, (connected directly without a plug cap), the results were the same

Lead direct to head produced no sparks

I'm unable to test the coil for internal breakdown as I don't have a resistance tester, but my gut feeling is this is the cause.

I'm not sure that the capacitor can be solely responsible as I don't get a good spark when I connect the coil directly to the battery and bypass the CB.

Johnny B - With regard to fitting a Brightspark condenser, are these available for coil ignition? the web site seems to indicate they're just for mag/dyno.

I'll update when I make some progress - soon I hope.

Regards Mick

My knowledge of micro farads is very limited.

Wrong, non existent, but I wouldn't have thought that there would be that much difference. I've fitted different car condensors (capacitors) to the Matchless at different times to get home but there didn't seem to be any difference.

Others will know better.

Johnny B

The size of the condenser is not that important. You just need to have one. It has two functions: one, it reduces wear on the points and two (most importantly) it creates a resonant circuit with the coil that causes the circuit to "ring" when the points open, creating a much bigger (longer duration) spark than you'd get otherwise.

Interesting experiment: disconnect the condenser and open the points. You'll see a big spark across the points, and a comparatively weak spark at the plug.

Hi

It's confession time.

After receiving a replacement coil and capacitor I re-visited the ignition issues. Cycling the new coil with the battery produced regular but still, in my opinion, weak sparks. With it fitted into the bike's circuit there were no sparks. Replacing the capacitor as well produced no sparks

More head scratching - I decided to break the circuit at the bullet connector under the engine / gearbox cover, Eureka! - healthy sparks indicating the CB assembly to be at fault. This was confusing as I'd tested it electrically before all the troubleshooting was carried out.

Finally identified the problem to be the fibre washer which isolates the sprung contact from ground - I assume, during repeated removal / fitting of the supply lead and capacitor the washer has failed allowing the sprung contact to ground, (rendering the CB assembly useless).
Made a new isolation washer from old aerosol top material and all is now fine - the sparks are much healthier which I assume is down to the capacitor now allowing the circuit to resonate, (thanks clanger9).

I now have a spare coil and capacitor, (which will ensure the longevity of those fitted), and am another step closer to the bike moving under it's own power

Regards Mick

PS: Johnny B, I still couldn't find a Brightspark equivalent, they all appear to be manufactured on back plates configured to mag / dyno systems.

Edit to say I've now been directed to the 'Easycap Universal' details - Thanks

Brilliant, well done for finding that one. Points don't often go shorted to earth, but there you go.
Glad to hear it's working again!