Surrounding the nozzle tube or hood is a curved restriction in the air intake passage, is known as a Venturi tube, which insures a constant relation between the air and fuel supplies. As the action of the Venturi tube is rather complicated, it will not be taken up in detail. Air is supplied to the Venturi passage through the intake (D). An annular float (K) surrounds the mixing chamber that acts on the gasoline supply valve (I) through a short lever arm. This valve is accessible for cleaning on the removal of the cap H that covers the valve chamber. Gasoline enters the float chamber through the fuel pipe G, and enters the spray nozzle through the two ports in the base of the mixing chamber.
The auxiliary air valve is a particularly novel feature of this carburetor, as no springs nor disc valves are used in its construction. Five balls (M) of different weights and sizes act as air valves, the balls covering the inlet ports (L) under normal operation. As the speed increases, the balls are lifted off their seats in order of their weight or size by the increase in suction. With a slight increase of suction, the lightest ball covering the smallest hole is lifted first, a further increase in suction lifts the next largest ball which still further increases the auxiliary air intake, and so on until at the highest speed all of the balls are off their seats. Access to the ball valves is had through the valve caps (N). The constant supply inlet is circular and may be set at any desired angle, as can the float chamber and gasoline supply connection. Control and adjustment are entirely by the needle valve.
(109) The Feps Carburetor.
The Feps carburetor has the main needle valve surrounded by a Venturi chamber as in the preceding case, the needle valve adjustment being made through a lever on the left of the mixing chamber. An auxiliary nozzle directly under the auxiliary air valve at the right, connects with the float chamber and furnishes an additional mixture of gasoline and air for hill climbing and high speed work when the leather faced auxiliary air valve lifts from its seat. The adjustment for this auxiliary jet is shown at the right of the air valve chamber.
For intermediate speeds, the air valve alone is in action. No controlling springs are used on the air valve which insures positive action and sensitive control of the air. A float surrounding the Venturi tube controls the fuel valve through the usual lever arm. A wire gauze strainer placed in the fuel chamber to the left prevents dirt and water from being drawn into the nozzle, and as this strainer easily removed it is a simple matter to clean and prevent the troubles due to dirty fuel.
By closing the upper valve in the vertical engine connection the vacuum is increased in the manifold when starting the engine. This increase of vacuum draws gasoline from the float chamber and primes the engine making the engine easy to start in cold weather. The tube through which the gasoline is drawn for priming is the small crooked tube bending over the float and terminating above the starting valve. Below this valve is the throttle valve which controls the mixture in the ordinary manner. The adjustment for intermediate speeds is made by the center knurled thumb-screw shown over the air valve chamber which controls the travel of auxiliary air valve. In effect this is a double carburetor, one jet for high speed and one for low.
(111) Gasoline Strainers.
Much trouble is caused in carburetors by dirt, water and sediment, collecting in the small passages and obstructing the flow of the gasoline.
Fig. 119. The Excelsior Carburetor in Which the Air is Regulated by a Ball which Lies in the Tapering Venturi Tube. An Increase of Suction Lifts the Ball and Allows More Air to Pass.