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Starts easily, stops during tick over and won't restart

Submitted by mike_haworth on Sat, 21/08/2021
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1959 Model 50.  The bike starts easily in the garage and ticks over for a while and then stops. Therafter it will not restart until it is completely cold again. The carburettor is new and has all the recommended jets  & standard settings. So, for now at least, I'm assuming the problem is electrical. The contact breakers have just been replaced. Less than 1000 miles ago the capacitor, the coil, the HT lead and cap and the plug were replaced.

What I have discovered (but this may be normal) is that the coil gets seriously warm although not too hot to touch. Also, holding it while the engine was running caused me to get a shock. So could the problem be the capacitor, the coil or the HT lead and is it possible to isolate which of these it may be  without replacing the lot ?  

Submitted by john_holmes on Sat, 21/08/2021

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Could be the coil is internally shorting when warm, been there and got 250 yards every 15 mins stop for a cool down on the flat, luckily most was downhill on route home so coasted for most of way. Holding the coil too tight in its bracket can crush the case and then short it internally, I wrap it in a piece of inner tube to stop that happening. As soon as the engine stops have you pulled the plug and then rested it on the head and checked for spark.

Submitted by philip_hannam1 on Sat, 21/08/2021

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This sounds to me more like a fuel issue.

Check the flow from the tank. Start with the tap, then connection tubing, carb filter and lastly float.

Submitted by andrew_sharp on Sun, 22/08/2021

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I once had a similar problem, which was caused by the points sticking open when warm, hope this helps

regards

Andrew

Submitted by alan_osborn on Sun, 22/08/2021

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Start the bike when cold-fine, then put a hot-air gun on the coil. You can get the coil too hot to touch (70deg) and it should still function. Take the cap of the points, check for opening/closing by eye. If not sure then set the points open and short them with a small screwdriver-should give a spark. Again running the bike cold and then hot-air gun on the points might show some thing.         But a coil shorting inside is highly likely.

Submitted by mike_haworth on Mon, 23/08/2021

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Hi All,

         Thanks for the feedback on my ignition issues. Lots to work through & try. Interestingly an article on this subject has been brought to my attention - 'Why ignition coils fail - common causes'. This is by Tony Proctor and was found in either the June or July issue of OBM. So this, along with the forum comments, will form the basis of my investigation. I'll report back if I identify a specific problem.

Mike

Submitted by geoff_drury on Mon, 23/08/2021

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This was exactly what happened to me once with a BSA A10.  (yes, I know)

Started fine from cold, but stopped and would not restart when hot.  Fine again when cooled down.

Turned out to be missing the insulation piece between the carb and the head.

A home made paxolin spacer cured it.

Just a thought.

Submitted by mike_haworth on Sun, 29/08/2021

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Model 50 now running as it should. The problems I was having were due to the coil being damaged. In my efforts to clamp it securely and stop any movement I had crushed the outer casing causing an internal short. This was evidenced by me getting a shock when holding the outer casing with the engine running ! So, with a new coil and a superior clamp for attaching it to the frame, the problem is solved. Thanks for all suggestions.

Mike

 



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