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Principals Of Operation - Carbureting
The basic purpose of a carburetor is to produce a mixture of fuel and air on which an engine will
operate; to do so relatively easy. However, producing economic fuel consumption and smooth engine
operation over a wide range of speeds creates the need for more complicated mechanism than a more
mixing valve.
There is an additional problem in that the price of such a carburetor must be held in
proportion to the price of the engine. The price of a small gas lawn mower engine is not much greater
than the price of the carburetor on an automobile.
Keeping this in mind, we utilize the
force of atmospheric pressure and the
principles of the venturi and the airfoil.
Atmospheric pressure may vary
slightly due to altitude or temperature,
it is a constant potent force which tends
to equalize itself in any given area. It
is the weight of the air in the
atmosphere pushing down and outward
in all directions and is commonly
figured as between 13 to 15 pounds per
square inch.
We know that air moves
from a high pressure area to a low pressure area.
To use this force of atmospheric pressure in a carburetor, we artificially create low pressure areas
and thus obtain movement either of air or of intervening fuel.
This will be illustrated later in the manual. The greater the difference in pressure between the two areas the greater the velocity or the greater the
distance we can raise the fuel.
In the interest of terseness we often use the terms vacuum or suction when we actually mean the difference in pressures.
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