Alan B. Pearce wrote:
>
> >My motorbike, and many others i guess, does the same. My
> >bike has 3 coils. Coil1 fires when piston 1 or 6 is on combustion, coil2 is
> >for 2 or 5 and coil 3 is for 3 or 4.  When the one piston is on combustion,
> >its mate is on exhaust. Its for emmision controls i think, or just to
> >simplify things a bit.
>
> This system has been used on motorbikes for many years that I am aware of. It is
> a minimisation of ignition components by having the high voltage winding on the
> coil totally floating. each end of the winding is connected to separate spark
> plugs, one on the cylinder under compression, the other on a cylinder in exhaust
> phase. By doing this only one coil is required for a two cylinder engine.

Yes Harley Davidson have done this since the 1920's,
used one coil for 2 cylinders.
Modern motors are starting to do this more, it's common
on motorcycles, where you don't want a distributor.
Some cars are following suit now, with V6 car engines
having 3 separate coils and no distributor.

But regardless of the coil windings remember that both
spark plugs always fire together, the designers rely
on 4-stroke motor ignoring the extra spark after the
exhaust stroke.
-Roman

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