BSA A10 ignition

[RDfella]

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.

[KeithJ]

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?

[RDfella]

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.

[KeithJ]

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?

[RDfella]

Yup, I understand science. Does anyone have the data and test figures to back up this power increase assertion?