>>>have a suitable once-around pulse of a couple hundred volts.  In most
>>>lawnmower type engines, the spark plug fires once per revolution; the
>>
>>Only the two-strokes (LawnBoy?).  Briggs engines fire every other time -
>>they're 4-strokes.
>>
>>Andy
>>


>    No way! 4-strokes machines also fires once per cilynder per revolution!!
>The difference is that 2-strokes combines the phases of Admission and
>Expansion in one stroke and Compression and Expulsion in other stroke!!! The
>spark plug fires everytime the motor hits the compression phase,
>independently of how many strokes your motor uses.

>    Rafael Pinto

Who told you this?

A 4-stroke engine has (you guessed it) 4 strokes.
Intake, compression, ignition and exhaust.

The complete prosess takes two revolutions of the engine. The spark plug
fires once in this period, ie every other revolution.

Should be easy to understand?

-Oyvind