Author Topic: A50 Misfire  (Read 87 times)

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Andy Edwards

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A50 Misfire
« on: 10 October, 2019, 19:40:44 »
Hello. I have recently converted my 1962 A50 from 6 volt positive earth to 12 volt negative earth. I fitted 12 volt coils, a solid state regulator/rectifier, an AGM battery, new HT leads, new spark plugs and I made a new loom to suit.  The bike has slowly developed a persistent misfire.  It starts easily and idles nicely but misfires under load.  I am convinced that it is an ignition fault. 

If I flick the points open with the ignition on I get a weak yellow spark across both sets of points.  With the engine running I get a strong blue spark across both sets of points. To me this suggests a problem with the condensers, but they are fairly new and have only run for about 300 miles. How likely is it to have both condensers fail? Are condensers sensitive to polarity?  If so, I should have fitted new condensers suitable for negative earth.

Any advice would be much appreciated.

chaz

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Re: A50 Misfire
« Reply #1 on: 11 October, 2019, 07:21:02 »
my old vauxhall viva had a condensor fail, I cycled 10 mile round trip to get a replacement one, 3 times I did the trip, all were faulty. in the end the shop gave me the card which I took home and tried until I found one that worked. it was 33 years ago and living in a village. the days when we had independant motor factor shops in towns like aladdins caves.

Andy Edwards

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Re: A50 Misfire
« Reply #2 on: 11 October, 2019, 11:16:59 »
Ah ok, I will have to try some replacement condensers then.

Andy Edwards

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Re: A50 Misfire
« Reply #3 on: 12 October, 2019, 20:15:42 »
Sorted, both condensers had failed!  I think I will carry spares from now on.

chaz

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Re: A50 Misfire
« Reply #4 on: 12 October, 2019, 21:23:22 »
http://nonlintec.com/sprite/cap_failure/

an interesting write up, I would think the vibration does not help and causes the breakdown and arcing.