[78-L] Fading sounds [fwd]

[Jeff Lichtman]

>I can recall gasoline-powered "threshing machines" thar worked the
>same way; the governor only allowed a spark when the speed had
>deopped below a given level. Thus. their sound was "bang" "whoosh,
>whoosh, whoosh, whoosh, bang!"
>
>Steven C. Barr

The governor on this type of engine (called a "hit and miss" engine) 
typically controls the exhaust valve, not the ignition. The intake 
valve opens by cylinder vacuum, not with a cam. The governor holds 
the exhaust valve open until the engine slows down to a set point, at 
which point it allows the exhaust valve to close. The cylinder pulls 
a vacuum on the next down stroke, which opens the intake valve and 
lets a charge in. The spark plug fires every other revolution 
regardless of whether there's a charge in the cylinder.


                        -        Jeff Lichtman
                                 jeff at swazoo.com
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