Author Topic: Why is the engine suddenly stopping?  (Read 1437 times)

Offline owain

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Why is the engine suddenly stopping?
« on: 08.11. 2017 20:58 »
I'm pretty chuffed with the way my A10 w/sidecar has been going since restoring the engine. The bike starts first kick and ticks over nicely when warm. However, occasionally the engine will just stop whilst I'm riding (usually after sustained riding at speed on the motorway). It can get me into some sticky situations and I'm not sure why it is happening. The odd thing is that as soon as I pull to the side of the road and wait a few seconds the bike will start straight up again with a kick. My thought is that the engine is getting too hot? Any ideas?
Sweden & North Wales
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'69 BSA A75R

Online Triton Thrasher

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Re: Why is the engine suddenly stopping?
« Reply #1 on: 08.11. 2017 21:09 »
Heat itself doesn’t make the engine cut out.  Can make it seize though!

First suspect is fuel supply. Is the tank cap vent blocked?

Does 600cc of petrol run out of the bottom of the carburettor in a minute, if you take the hex jet cover off?

What do you use for an ignition system?

Offline t20racerman

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Re: Why is the engine suddenly stopping?
« Reply #2 on: 08.11. 2017 21:10 »
Sounds like a carb icing problem. Not known that on an A10 before, but that's exactly what happens when it occurs.
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Online Triton Thrasher

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Re: Why is the engine suddenly stopping?
« Reply #3 on: 08.11. 2017 21:14 »
Sounds like a carb icing problem. Not known that on an A10 before, but that's exactly what happens when it occurs.

That’s a really good suggestion. More likely on a damp morning.

Shouldn’t be a sudden stop though.

Offline t20racerman

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Re: Why is the engine suddenly stopping?
« Reply #4 on: 08.11. 2017 21:34 »
My Volkswagon Polo used to do just that. Stopped when it felt like it, usually in the colder mornings, and after waiting a couple of minutes, it restarted and ran perfectly.
1961 A10 - somewhat modified :-)
1980 TZ350 - lunatic Classic Race machine
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph 675 Speed triple
Ossa 250 and yet another T20 racer in bits both being built up

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Offline owain

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Re: Why is the engine suddenly stopping?
« Reply #5 on: 08.11. 2017 21:41 »
I have an amal concentric carb fitted to the A10 plunger in lieu of the leaky remote float carb. It's bit difficult to measure flow rate out of the carb though as there is no drain plug at the bottom of the float. The tank cap vent isn't blocked. I'd assume that a seized engine would cause the back tire to stop rotating and that the bike wouldn't kick over so freely when stopped. I'm running the lucas K2F magneto with auto-advance and NGK B6HS spark plugs for ignition.
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Online Triton Thrasher

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Re: Why is the engine suddenly stopping?
« Reply #6 on: 08.11. 2017 21:52 »
Are the gauze strainers in the tap and carb banjo clean?

Offline owain

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Re: Why is the engine suddenly stopping?
« Reply #7 on: 08.11. 2017 21:56 »
There is petrol flowing freely from the taps and when I last disassembled the carb (about 3 weeks ago) the banjo gauze was clean
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Online morris

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Re: Why is the engine suddenly stopping?
« Reply #8 on: 08.11. 2017 22:02 »
Makes me think of what happens when I forget to turn the fuel tap on.
Engine suddenly cuts out without warning but when turning the tap back on and wait a few seconds for the fuel level  to rise it starts first kick.
Happened to me  last sunday... *eek*
So I would bet on the fuel level in the float bowl getting to low.
Have you tried running with both taps open?
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Offline owain

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Re: Why is the engine suddenly stopping?
« Reply #9 on: 08.11. 2017 22:08 »
Both taps are always open but perhaps the float bowl is set too low. It does take a fair while to prime the carb before starting, perhaps another indicator of a low float?
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Re: Why is the engine suddenly stopping?
« Reply #10 on: 09.11. 2017 11:05 »
Both taps are always open but perhaps the float bowl is set too low. It does take a fair while to prime the carb before starting, perhaps another indicator of a low float?

It's unlikely.....but maybe check the fuel is not being prevented from entering the float chamber due to a blocked float chamber vent, I'm not sure where the vent is on a concentric, on a monobloc the tickler is the vent.
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Offline jachenbach

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Re: Why is the engine suddenly stopping?
« Reply #11 on: 09.11. 2017 12:19 »
I wouldn't rule out an electrical problem, particularly the wire to the kill switch. Driving a sidecar, you'll be turning the handlebars to pull to the side of the road and to straighten the rig out once off the road. I'd look to be sure there is adequate slack in the wire and that it hasn't rubbed through in the area of the steering neck. In my experience fuel starvation gives a bit of warning, such as rough running or lack of power before actually stopping completely.

Offline owain

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Re: Why is the engine suddenly stopping?
« Reply #12 on: 09.11. 2017 15:31 »
Engine stopped suddenly again today. I can potter around town all day on the bike with no problems but as soon I'm going at full speed in 4th gear on the motorway (about 50-60mph is an estimate gauging by the speed of passing cars; as I have no speedo fitted at the moment) the engine will suddenly shut off after maybe 3-5 mins of motorway riding. Today the back wheel also stopped dead as well, I'm not sure if this was because of me accidentally pressing on the rear brake in a panic or due to the engine issue. Regardless, as soon I get to the side of the road...tickle the carb and kick, it starts right up again. However, when I start the bike up again it did die a few seconds later again.

I'm going to let the bike sit in the garage now and take off the carb this weekend to inspect it but it seems like a very strange thing for this to only occur during only motorway riding :/

Any thoughts on the spark plug type playing a role? I'm running NGK B6HS, perhaps a colder plug e.g. B7HS/B8HS?
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'69 BSA A75R

Online Greybeard

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Re: Why is the engine suddenly stopping?
« Reply #13 on: 09.11. 2017 17:19 »
Engine stopped suddenly again today....
I think a partial seizure would be indicated by a very hot engine making hot smells and a cloud of smoke when you stopped. Has the mag been overhauled?

Online bsa-bill

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Re: Why is the engine suddenly stopping?
« Reply #14 on: 09.11. 2017 17:25 »
Quote
Any thoughts on the spark plug type playing a role?

Would be a bit of a coincidence for both plugs to fail at the same time, could be a fault somewhere in the magneto tho
All the best - Bill
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