Britbike forum Forums British Motorcycle specific Brands Ajs & Matchless forum 350 16m

Hi all, got a ajs 350 16m to play with, haven't been on the road yet but have a starting problem, put new plug in, started 1st time, run it for about 15 minutes, turned off and couldn't get it started again, took plug out seemed OK but was very hot, any thoughts would be much appreciated, it's a 1957

Hi Bob,

Welcome!
The reasons could be varied. When you had the plug out, did you check you still had spark? Is it magneto or coil ignition? When you ran it, do you mean idling on the stand or did you ride or around? Is there an insulation block between the carb and manifold?

Adrian

Hi thanks for your reply, checked plug, first kick, spark, 2nd kick, weaker spark, 3rd kick no spark, it's magneto ignition, had it idling and ran it up and down the drive, insulation block? Don't know

15 minutes of running just in the driveway with little movement could have got it very hot in the engine dept.
And in the magneto dept ?

What is the history of this - is it supposed to be a good runner.
Or recently 'restored'. ? (without doing anything to the magneto !!).

Sparks disappearing when the maggie gets hot is a classic symptom of a failing condensor.
Buried deep inside the maggie.
Difficult to impossible hot starting.
Met this a while back = magneto overhaul time.
Whole reams have been written on this subject.

Matchman62 is referring to the insulator block that keeps the carb from overheating.
And causing vapour lock. This would be additional to the sparks disappearing, however.
Hopethishelps.

P.S. ALWAYS test with a new spark plug, however.
Whole armies of folks have probably dealt with a dud or dirty or dodgy spark plug over the eons ....
And if the idling mixture is a bit rich, it could get dirty quite quickly.

May we assume you’ve done the obvious service items, such as contact breaker points?

Hi, thank's for your reply, I don't know much of the history of the bike, but apparently since my first post,I've found out that the engine was supposed to have had a rebuild and converted to 12 volt, but I haven't checked it out yet, I'm already getting a bit despondent with it and think I've bitten off more than I can chew!!

Just a thought, if there is a problem with the magneto does it ruin the plug, will it start with another new plug, will it ruin the new plug, as you can tell I'm not very up on electrical issues, give me mechanical problems any time

Rather think of it as an opportunity to learn lots of new skills !
If you can already start it, then you are ahead of many owners.
I've heard of owners selling up because it wouldn't, or they couldn't....

When I bought an old dommie as a lad, I knew NOTHING much about anything mechanical.
It sure taught me lots ...
The maggie that was in it was junk, didn't take very long to figure this out, or then improve it.
You aren't born knowing this stuff, knowledge has to come from somewhere.

The Owners Handbook has a section in the back of all (?) the ills you might encounter.
Remember, these were sent out to the colonies, and petrol had water in it, dust was a normal hazard,
and changing ruined or punctured tyres was expected on every trip ....

A weak maggie might soot up a new plug.
Without a good clean, it might not want to talk to you.
Tweaking the idle so it runs cleanly and evenly is a skill to be worked at.
Running it around the block so it gets some cooling is also helpful in this process.
And you can judge any progress by how much it improves each time.

Knowing if the maggie was rebuilt might also be useful.
Can you enquire of the previous owner about this ?
This is (often ?) skimped on in rebuilds, if it seems to spark

P.S. If you can get it running, take it for a quick run around the block, or neighbourhood. ?
It might just need some 'clearing out of the cobwebs' ?
And moving keeps it cool, so the sparkplug/maggie may not shut up shop ?

I regularly see a chap in an old MG doing 5 or 6 laps of the block here,
I figure that he's just keeping it ticking along ...

And if the maggie clags out doing this, make sure you can coast downhill back home !
You'll know what needs more specialist attention then ....

Hi Bob and welcome,

Too rich mixture or excessive oil consumption are what usually fouls (ruins) a plug. A weak mag will have trouble firing a fouled plug.

But, did you check the plug gap before you installed it? These old mags like a much narrower gap than modern ignitions and the plugs you buy these days are usually gapped too wide. Check it and if needed, gap it to .018" to .020". (.020" is very close to .5mm if you think better in millimeters.)

The next thing to verify is breaker point gap and cleanliness. It's usually best to first clean the points with some fine wet or dry sandpaper and then a small piece of white business card wetted with gas, carb cleaner , brake clean, what ever you have handy. The card will get dirty each cleaning so repeat a few times until the card stays clean. (Snip off the used part each time.)

Then, rotate the engine while closely watching for when the points are open the most. That is where to check the gap. It should be .012" (.3mm) or even a slight bit wider, especially for an old used mag that probably has a worn point cam.

But this is where it starts to get tricky, if it didn't seem tricky enough already, as there are a few different types of mags out there. The usual Lucas mag will have a fixed point on a threaded post that requires the tiniest of wrenches to do the adjustment. There isn't really a substitute. You will see what I mean when you get a close look at it. Cross that bridge if you need to or maybe find someone local to you that can help..

So anyway, there's a few things to chew on to help you decide if you are up for more.

One more thing.
Check and top up your oil levels but with a warning. The engine may be wet sumped from sitting unused. So have a look in the tank. If it is a third to a half full, run it that way but then look inside while it is running to be sure oil is being pumped back to the tank. After a few miles riding, all the oil will be back in the tank and you can then add a little if it needs it. The best thing really would be to drain the crankcase and top up the oil tank with fresh oil.

Best of luck..

Hi ,thank's for your reply, gapped the new plug to 20 thou (I'm old school) I've decided to get a new condenser so will check the points when I fit it, from what I've seen you just remove the front plastic cover from the mag and the points and condenser should be looking back at me. I'll do that and see if it makes any difference.

If you were truly Old School you would know the proper plug gap for the Lucas magneto is .018". It could be less if you were having problems with the magneto
John

Ah, that means you have a Lucas SR1 magneto.
A rotating magnet type.
Much easier access and to change the condensor, like you say.

Yes spark plug gaps are smaller with magnetos - gives them (the maggie) an easier life.

Bakelite = plastic

ive never found a wire spark plug gapper smaller than 0.020-inches.

i use flat feeler gauges, but it irks me that technology has left magnetos behind.

For precise gapping you could use a drill shank Kevin. A No 77 drill is 0.018” or a .045mm drill is .0177”. Storing them is a bit of an art form as they are easily lost or swept up and thrown out with the rubbish. It took years for me to get the message across to my family that those odd little packets and tubes contained serious stuff so don’t touch. Blood sample vials were useful in the past but changes in collection methods have put the brakes on that one. I’m sure you’ll find a way.

Cheers,

thats a very good idea.

i store tiny bits in cigar cases or little plastic vials like thise used for mechanical pencil leads

Hi Bob,
Expat Steve here, one of my bikes owned for nearly eight years is a 1960 G3 Matchless so no magneto, though joining the Brit AMOC club and their forum has taught me everything I know about the bike, as previously my knowledge was zilch, so understand how you feel.

I’m not much use helping with your starting issue but from reading scores of posts on that forum, I would humbly suggest the guys here have got it right regarding hot starting magneto issues, particularly concerning the condenser.

One other point that comes up repeatedly, among scores of others on the Jampot forum, is that modern spark plug ceramic insulators are not glazed as in times of old, so the time honored method of cleaning using a wire brush produces scratches on them which leads to current tracking to ground (earth!) instead of producing a spark. Not suggesting that is the issue with your bike, just passing it on as may be useful in the future.

Hang in there and keep communicating here for great advice and support and you will get it sorted in time I’m sure.

I've never mentioned the gap for the points, .020 is what I said for the plug gap

It may not have been crystal clear, but plug gap is indeed what was being discussed. (?)
John is one of the/our most experienced hands.

I'd comment though for my Norton Dommie, the magneto points are 0.012" and the spark plugs 0.015"
K2F maggie, different plugs though.
And thats printed in b&w in the manual.
(my Ajay is for show only at this stage, still needs work...)
(and has an N1 maggie anyway)
Always read the manual for whats applicable for YOUR bike.

And Lucas would sell you a 0.015 gapping tool.
https://encrypted-tbn0.gstatic.com/...rLUgCMdqIU9oF7jo2Q-ioP5iG4Q&usqp=CAU

https://content.invisioncic.com/r27...JPG.12d7e32b6e0f401106a527c3aa409c72.JPG

Sorry for the misunderstanding, I thought John's post referred to the points gap, as for "old school " I meant I use inches not mm, maybe John misunderstood my post, hey ho happens to the best of us. Will update when new condenser arrives and I've fitted it, fingers crossed 🤞

I don't think John misunderstood anything .
A wider spark plug gap puts more stress on the Magneto .
He was recommending you close the spark plug gap .
In free air , the voltage difference between .018 and .020 is only 152.4 volts
but when you put the same gaps under compression , with fuel
The difference ( by my rough math ) jump to between 1000 and 1500 volts .

got any pictures? i remember lots of ajs from growing up in the colonies.

havent seen one in a long time

I think there is another misunderstanding brewing here !!!


Are you sure about that 0.4 volts ?? !!
A humid or dry day would likely change that - by quite a bit.
My physics tutor would be having kittens about that 0.4 volts...
And even the 2 volts.
Can we say ~150 volts, +- 50v ??

Other than that niggle, we understand you loud & clear ...

John's post referred to the gap for a Lucas magneto, I just assumed he was talking about the points gap in the magneto not the spark plug gap

If you have to look for an Old School tool you just have to look in one of my tool boxes. The wires are used to set plug gap, the slotted tool is used to bend the plug's electrode. There are two types of feeler blades: One plain one to set the point gap and stepped ones to check the tappet clearance. You see from the patina that it has seen a lot of service over the past 50 years.

The typical plug gap for a Lucas magneto and later Lucas systems used on the racing ignition used on many BSA and Triumph (read Triumph TT and C models) is 0.018".

Opening and closing the point gap changes the the Dwell and ignition timing a few degrees.
The typical point gap is .012" to .015" (.015" typically used when setting up the magneto timing). It can be varied to change the ignition timing and point dwell on the fly. Handy when making last minute tuning adjustments at the Track, or checking to use when diagnosing magneto problems in the field.

A set of plug gauges is a handy tool for both checking carburetor parts and setting the gap on used spark plugs.
Old School revisted.