AJS & Matchless Owners Club

Hello,

I've remobilised my Triumph T21 twin since the big end went on my Matchless G3 in June. Felt I needed replacement 2 wheels while I try to get the Matchless repaired. I had to rebuild the top end with new pushrods, reground valves, new springs and gaskets etc. Starting is much improved and the engine runs really sweetly.

Took it for a spin and all is great for several miles, then the engine starts to run unevenly, looses power and finally stops. Restarting isn't possible, but the engine will run very unevenly on EMG setting ... dies if I switch over to normal IGN position on the ignition switch.

If I leave the engine until it has cooled for 15-20mins, it will start up easily and run sweetly. Drive off for another few miles and it all repeats again. So it seems to be temperature related - possibly faulty insulation on a coil or condenser ... but they're recently renewed, so I feel unlikely to be the source of the problem. Frankly, I'm stumped.

Has anybody any thoughts on what might be the problem or any suggestions from their own experiences?

Bruno

Only thing that comes to mind is my old Norton 16h would do exactly that run for few miles then stop, cool down and run okay again, The reason was I had been very mean with the tappet clearance to make it sound sweeter, so checked and adjusted tappets correctly and all was fine till I rode it into a river, but that's another story.

Colin

Have you checked that the petrol tank cap breather isnt blocked? it can give just those symptoms (dont ask how I know)

Sounds very much like a dud capacitor to me. Never had it happen on a bike but have had a few go on cars years ago. Runs OK but plays up when hot then dies. When cooled down will start again and seem OK until it gets warmed up again. Always been a capacitor on the way out. Happened once with a brand new replacement after very few miles.

is it a 60s bike with alternator and coil ignition .
i ask because you mention EMG setting and this is taken direct from the alternator for when the battery goes flat but is only for starting in emergencies.

my ariel leader conked out one winter night back in 1982 and i got it going on EMG setting but it failed soon after , then my dad told me i should only use EMG for starting and switch over immediately to normal running otherwise i would burn out the alternator .
guess what , i had burned out the alternator and it had to be replaced .

i would first check your battery is good and wiring from it isnt shorted to frame , then check or swap the alternator .

you say engine runs for a while then starts to splutter etc and misfire , this is a thing that will happen on coil ignition when the battery goes flat .

maybe the alternator is breaking down once its got warm or run for a while , but if you leave it , it will work again for a short time for some reason .

you probably only need to bother about the stator , as the rotor is probably fine .

hope you get it sorted .
ian

Hi

What's the charge state of the battery like? Can you power the lights immediately after the engine comes to a stop? You may have a bad battery or charging circuit.

Regards Mick

Thanks for the helpful suggestions gents ... it's a tricky one and I sense it is going to be a process of elimination.

For sure the tappet setting is spot on and has been re-checked several times. The battery is fully charged and a sealed 6v unit, about 2 years old and in good condition. So that's a couple of leads hopefully OK.

Les, your suggestion about the petrol cap breather - definately worth a check as it has blocked before, but then the engine just died in a classic 'petrol starvation' fashion. What's happening at the moment is that the engine seems to want to keep running and struggles on for quite some time before giving up the ghost!

I'm tending to sway towards an electrical issue which I feel least competent working on (even though I've ended up doing a lot). I will check the earthing and wiring carefully, as well as the condition of the coil and condenser (it is indeed a 1963 vintage T21 and alternator/coil ignition). Both these components are brand new, but I'm guessing that counts for little these days and they could still be faulty. I know how to check the resistance on the coil, but can anyone suggest a easy way to check the condenser (other than changing it)?

Will let you know how I get on ...

Bruno

Do you have an ohm meter? If so, you can do a rough check on the condenser. It should initially show near zero ohms, before increasing to megohms within a second or two (as the condenser charges). Reverse the test leads and it should do the same thing again.

If it shows significant leakage when charged (in the kilo-ohms region or less), then the condenser is u/s.

Unfortunately, faulty condensers have an annoying habit of only playing up when hot and they can revert to perfect behaviour when cold. Easiest check is to replace it - I've had "new" condensers fail almost immediately, others can last for decades...

Hi

Unless you are proposing to check the capacitor immediately after the engine has failed I think your going to have problems / false outcomes.

Doesn't your Matchless have a capacitor? Why not substitute it as a known 'good' component and see what effect it has?

Still not convinced though - if it were the capacitor I'd expect the effect to be the same on EMG.

Regards Mick

Thanks for the suggestions and perspectives Clanger9 and Mick. I think it makes most sense to just try another condenser unit - unfortunately my Matchless came with electronic ignition and I've never followed through on my intention to revert back to contact breakers etc.

Anyhow .... I do still have the old condenser I replaced on the Triumph when I put in new contact breakers. While I wait for a new one, I'll give it a try and see what happens - it wasn't faulty when I changed it out. Please don't ask me why I changed it .... seemed like a good idea at the time.

Cheers, Bruno