Why is the engine suddenly stopping?

[chaterlea25]

Hi Owain,
What type of taps are fitted?
There were some on the market where the seals expanded and restricted flow drastically
Pull the fuel pipe off the carb and check the flow

John

[Triton Thrasher]

the back wheel also stopped dead as well 

That does happen when the engine seizes.  Can you see any of the cylinder bore, through the spark plug hole?

[a10 gf]

Generally, if it's really sudden \ abrupt \ instant, I would look at ignition (magneto) 1st. I'd remove magneto and run it of a drill with plugs connected, and see if it does anything strange after a while or at high rpm. Heat it up with a warm air gun to simulate real life. If impossible to trigger any fault, then look at other possibilities.

Fuel starving in my experience gives a somewhat more gradual loss over some seconds, nothing instant.
About seizing, first shows some symptoms, and not an instant cutout ? (got no experience there ...thankfully).

But with backwheel locking up something is seriously wrong ...yes, look for signs of seizing, and I'd stop riding it until the fault is located and fixed. Safety first.

[owain]

Cheers for the help guys. I've got the flat slide type of petrol taps on the tank. They are the original ones from 1950 (I've just replaced the cork washers inside). Petrol gushes out of the taps when I open them.

I've removed the tank and spark plugs to see if I can have a look at the cylinder walls. It's a very small area that I can view but can't really see anything out of the ordinary. I gently ran a screw drive over the cylinder to dry and detect any edges but I couldn't feel any ridges/ deep scratches. I'm not totally sure what the symptoms are of a partial seize on the cylinder wall though. I'm pretty sure the oil pump is working as I inspected the oil tank after use and the oil in the tank was hot i.e. circulated back from the engine. However, the bike will wet sump within a few days if it's left to stand. So I've installed a anti-wet sump valve (one that I must be manually opened but does not restrict oil flow...unlike those spring release anti-wet sump valves)

I've totally restored the engine, gearbox and clutch (bored cylinders, cleaned sludge trap, ground the crankshaft, etc) this summer but didn't touch the magneto or dynamo as both appeared to function. The last time this motorcycle was on the road before I had it was 1966 and I assume the bike hadn't really been given any attention since.

[Triton Thrasher]

I wouldn’t trust a magneto that was wound 50+ years ago.

But- seizure after a too-tight rebore is depressingly common too.

[owain]

I've just read on the Norton owners club website a member that posted "You can cook a newly rebuilt engine with a duff mag as if it does not spark at the correct temperature your engine will overheat and be a pig to start when hot.".

I had always assumed that a spark is a spark...:/

[duTch]

 

.... So I've installed a anti-wet sump valve (one that I must be manually opened but does not restrict oil flow...

 

 

.I had always assumed that a spark is a spark...:/.

 Not always the case...damhik 

 As mentioned above, fuel starvation due to low bowl fuel level.....

 Richard L had a thread of a similar nature,  maybe rectified by a bowl modification... have a search for that- I'll try same 

[bsa-bill]

I had always assumed that a spark is a spark

A spark is a spark in 15LBs per SQ inch atmosphere but not necessarily  in a one compressed 9  times or so

[Shark]

Owain, your problem sounds the same as one I have just resolved. Read this, it may help you sort it.www.a7a10.net/forum/index.php?topic=10874.0

[duTch]

 Needs to be in a live hyperlink thingy to work without copy&paste


 www.a7a10.net/forum/index.php?topic=10874.0
Report t

[Shark]

Thanks duTch

[BSA_54A10]

Get a pair of in line spark testers ( the red neon tube type ) or a pair of those glowing spark plug caps.
Next time it stops dead have a quick look at the testers.
No flashing = electrical problem
Flashing all the way till the engine stops = fuel problems.
Could be something really stupid like a dirty pick up contact, loose magneto ground wire or wrong brushes in the magneto .

I had an A 10 with Bosch brushes fitted and it would run for a set amount of time then stop.
I would get off and fiddle with a few things then it would start again & run for another 1/2 to 1 hour.
Eventually I found out that if I just stopped for 10 minutes or more it would fire right up if I did nothing so I just started pulling up for a fag.
No one twigged and I did not either till I walked into an auto electrician asking for a new pair of brushes to replace these ones on my BSA.
he described the exact problems I was having and sold me some Lucas one then the problem went away.

In any case working out if it is electric or fuel has you 1/2 way home.
Get some 900 series bowls as they have the drain plugs in the bottom.

[Rex]

The "problem" with going down the electrical route is that wrong brushes, loose earth wire etc would generally cause problems at any speed, while the OP's problems show after 5 minutes on the motorway (or whatever the exact scenario was).
Everything needs checking, that's certain, but the symptoms aren't consistent with the usual electrical gremlins.

[duTch]

 I'm inclined to go with fuel starvation,  given that you're hauling an outfit at highway speed.
 That would up the consumption for starters and if you have sidecar gearing,  the extra revs  will be sucking even more

 And given the discussion of Richards issue  that I mentioned earlier.....

[bikerboy]

I would be very concenred thats its partial seizure, electrical and fuel problems are inconvenient, partial seizures are expensive