Author Topic: BSA A10 ignition  (Read 12285 times)

Offline RDfella

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Re: BSA A10 ignition
« Reply #45 on: 24.07. 2020 20:00 »
I wonder how many simply put plugs in without checking the gap? On cars, always used to be .025" and most plugs came pre-gapped to that. But nowadays, with electronic ignition, some plug gaps are 1mm or more (.040" +). Not with old magneto-ignited bikes. I believe the recommended gap was .017" - at least that's what I've always used.
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.

Offline KeithJ

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Re: BSA A10 ignition
« Reply #46 on: 10.08. 2020 18:54 »
Just dropped my plug gap to 0.010" and is easier to start.  Also starts more consistently on the electric starter.

If having a cluster of sparks increases power output significantly, what performance is lost, if any, by reducing the plug gap by about 50% on a mag?

'59 A10RR + Second engine

Offline RDfella

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Re: BSA A10 ignition
« Reply #47 on: 10.08. 2020 19:34 »
I would doubt a cluster of sparks would increase power by a measurable amount, never mind significantly. Might ensure more complete combustion with today's weak mixtures (which I believe was the purpose) but unless the combustion chamber is an awful design, can't see what difference it'd make with normal fuel / air ratio. As for reduced spark gap for magnetos, it may slightly reduce performance, but then if you can't start it there's zero performance. Again, I believe the purpose was to ensure a more reliable start, given a magneto's weak spark, especially at kick-starting revs.
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.

Offline KeithJ

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Re: BSA A10 ignition
« Reply #48 on: 10.08. 2020 21:16 »
I would doubt a cluster of sparks would increase power by a measurable amount, never mind significantly. Might ensure more complete combustion with today's weak mixtures (which I believe was the purpose) but unless the combustion chamber is an awful design, can't see what difference it'd make with normal fuel / air ratio. As for reduced spark gap for magnetos, it may slightly reduce performance, but then if you can't start it there's zero performance. Again, I believe the purpose was to ensure a more reliable start, given a magneto's weak spark, especially at kick-starting revs.

Just going on from what  BSA_54A10 said on an earlier post:

A customer fitted one to his T100 and found it to be overheating due to running lean.
HE also found a big increase in Hp to the point that the clutch could not cope.
Now this was not a std bike as he was into Vintage Moto Cross & Trials so lots of revs with little cooling breeze
HE converted about a dozen more and the singles did not seem to have the same problem but he went up a jet size or two right from the start.

So still don't understand?


'59 A10RR + Second engine

Offline RDfella

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Re: BSA A10 ignition
« Reply #49 on: 10.08. 2020 22:01 »
Yup, I understand science. Does anyone have the data and test figures to back up this power increase assertion?
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.