[SEL] Flywheel dangers

[John Culp]

> Before he sold it, we ran Dave Rotigel's 12 hp T/G Hercules on kero.  
> That
> engine was DEFINITELY happier running on kero than running on gas.  It 
> ran
> steadier, generally firing every 4-stroke cycle and had a softer, more 
> mellow
> exhaust note.  On gas she'd often fire every other 4-stroke cycle and 
> had a
> much sharper bark.

That, paradoxically, is because it's running less efficiently on 
kerosene. The engine slows down and opens its throttle valve a little 
more, which lets in enough fuel-air mixture to make a combustible 
mixture with the noncombustible exhaust gas remaining in the clearance 
space of this low-compression engine. On gasoline it speeds up more 
with a power stroke, the governor responds by closing the throttle 
further, and the small amount of fuel-air mixture is too diluted by 
noncombustible exhaust to fire. As the engine goes on through its cycle 
and flushes that charge out, the next one is combustible AND contains 
part of the fuel-air mixture that was admitted on the previous cycle, 
so it makes a bigger "explosion" in the cylinder, and it repeats. 
8-stroking. The sharp "bark" every other cycle is because more fuel is 
burning than would be if it fired every cycle. Sometimes you can get it 
to settle down and hit every lick while idling on gasoline, and it'll 
quieten down more than it will on the slow-burning kero.

John Culp
Bristol, Tennessee, USA