Fig. 28. Stromberg Carburetor Model M—Accelerating Well
When the motor is idling or retarding in speed, the accelerating well or space “F” fills with gasoline. Now when the throttle is opened, thereby increasing the suction in the venturi tube, the following takes place: atmospheric pressure at the bleeder “C” exerts itself on the gasoline in the space “F” forcing the liquid down to join the regular flow from “H” and passing up the space “B” and out into the high velocity air stream through the small venturi tube. While the well acts the flow of gasoline is more than double the normal rate of flow, thereby compensating for the lagging of the gasoline referred to previously.
Upon close observation it will be noticed that there is a series of small holes down the wall of the well. Referring to the analogy of the U tube, these holes directly connect the two arms of the U tube. It is obvious that the smaller and fewer these holes, the faster will the well empty, due to the U tube suction, and the larger and more these holes, the slower will the well empty. It is therefore apparent that the rate of discharge of the well can be regulated as required by different motors, different grades of gasoline, different altitudes, etc., by inserting wells of different drillings. The action of the well is also dependent upon the size of the hole in the bleeder “C” because it is the relative area of this hole in the bleeder as compared to the area of the holes in the well which determine the rate at which the well will empty.
The foregoing characteristics of the model M carburetor have dealt more with the open throttle or high speed operation. We shall now consider the operation when the motor is idling. Earlier types of carburetors, when high test and very volatile gasoline was employed, were designed with a mixing chamber in which the gasoline, after being discharged from the nozzle, would mix with the air and evaporate very freely. Present day gasoline, however, is considerably heavier and very much less volatile, and we therefore cannot depend upon its volatility to accomplish its vaporization.
Fig. 29. Stromberg Carburetor Model M—Idling Operation
[Fig. 29] shows the arrangement and idling operation of the model M Stromberg carburetor. Concentric and inside of the passage “B” is located the idling tube “J.” When the motor is idling, that is, when the throttle is practically closed, the action which takes place is as follows: the gasoline leaves the float chamber, passes through the passage “H” into the idling tube through the hole “I,” thence up through the idling tube “J” to the idling jet “L.” Air is drawn through the hole “K” and mixes with the gasoline to form a finely divided emulsion which passes on to the jet “L.” It will be noted that this jet directs the gasoline-air emulsion into the manifold just above the lip of the throttle valve. Inasmuch as this throttle valve is practically closed the vacuum created at the entrance of the jet “L” is very high and exceeds 8 pounds per square inch. It is obvious, therefore, with this condition existing, that the gasoline will be drawn into the manifold in a highly atomized condition. It is well to call attention here to the fact that the low speed adjusting screw “F” operates a needle valve which controls the amount of air which passes through the hole “K,” and it is the position of this needle valve which determines the idling mixture.
Fig. 30. Stromberg Carburetor—Throttle 1⁄5 Open
As the throttle is slightly opened from the idling position a suction is created in the throat of the small venturi tube as well as at the idling jet. When idling the suction is greater at the idling jet, and when the throttle is open the suction is greater at the small venturi tube. At some intermediate position of the throttle there is a time when the suction at the idling jet is equal to that at the small venturi, and, therefore, at this particular time the gasoline will follow both channels to the manifold. This condition which is illustrated in [Fig. 30] lasts but a very short while, because as the throttle is opened wider the suction at the small venturi tube rapidly becomes greater than that at the idling jet. The result is that the idling tube and idling jet are thrown entirely out of action, the level of the gasoline in the idling tube dropping as illustrated in [Fig. 31], where the throttle is shown to be wide open, in which case all of the gasoline enters the manifold by way of the holes in the small venturi tube.