From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Guide on the operation and adjustments of the automatic choke control for a Stromberg carburetor.
| Identifier | ExFiles\Box 122\3\ scan0209 | |
| Date | 1st January 1940 guessed | |
| CADILLAC 1940 STROMBERG AUTHORIZED BENDIX STROMBERG CARBURETORS SALES & SERVICE CARBURETOR AUTOMATIC CHOKE CONTROL GENERAL DESCRIPTION The automatic choke control is built into a housing integral with the carburetor. The principles used in the operation of the automatic choke are manifold vacuum, thermostat spring, and an offset choke valve in the carburetor. The vacuum piston and thermostat are directly connected to the carburetor choke valve and accurately control the opening and closing of the choke valve under varying operating temperatures and at various throttle positions. A tube leading from the exhaust manifold to the thermostat chamber transmits heat to govern the tension of the thermostat spring. A fast idle cam operating in conjunction with the automatic choke provides the proper throttle opening for a cold engine and thereby prevents the engine from stalling during the warming-up period. OPERATION AND ADJUSTMENTS CHOKE CLOSED—FAST IDLE—COLD ENGINE—FIG. 1 When the engine becomes cold, the thermostat "B" also cools and gradually gains tension. The thermostat is unable to close the choke valve "A" until the throttle is opened. It is therefore necessary to depress the accelerator pedal slightly and then allow it to return to normal position before making a start. Opening the throttle in this manner permits the throttle stop screw "E" to be moved away from the fast idle cam "D.{John DeLooze - Company Secretary}" This allows the choke valve to close in accordance with the thermostat tension. The throttle stop screw then comes to rest on a higher lobe of the fast idle cam or on the ear of the loose lever "F" if the choke valve is completely closed as shown in Fig. 1. This provides the proper throttle opening for the prevailing engine temperature. The choke valve "A" is held in closed position during the cranking period by the tension of the thermostat "B". CHOKE PARTIALLY OPENED—ENGINE RUNNING—WARMING UP PERIOD—FIG. 2 When the engine begins to fire, the manifold vacuum thus created pulls the vacuum piston "C," opening the choke valve "A" against the tension of the thermostat "B." Sufficient air is thereby admitted to give a satisfactory running mixture. When the engine continues to run, it is necessary to open the throttle slightly, which procedure ordinarily occurs when driving the car away. If the car is permitted to stand and idle, the throttle should be opened slightly and then allowed to return to slow idle position. As the choke valve opening is increased, the fast idle cam "D" is allowed to revolve so that the throttle stop screw "E" comes to rest on a lower step when the throttle is opened and then permitted to close. ENGINE WARM—CHOKE WIDE OPEN—SLOW IDLE—FIG. 3 While the engine continues to run, the amount that the choke valve is opened against the tension of the thermostat spring "A" is governed by the quantity of inrushing air past the off-center choke valve and the travel of the vacuum piston "C." Heat is transmitted into the thermostat chamber by hot air being drawn from the "stove" on the exhaust manifold. The thermostat gradually absorbs sufficient heat until it does not offer any further resistance to the choke valve opening. At the same time the fast idle cam "D" rotates until the throttle stop screw "E" is at normal idle position. FIG. 3. The throttle stop screw should be adjusted for a car speed of 7 to 8 miles per hour with the engine at normal operating temperature. NOTE: The torsional spring of the fast idle loose lever has one end connected to the fast idle rod. When servicing, it is very essential that the bushing is placed on the rod after the rod is assembled in the lever. The hook of the spring should be assembled on the rod with the end of the hook butting against the ear of the lever as illustrated in FIG. 3. It is also essential that the lever and cam move freely and that the rod does not stick or bind in the slot of the lever. DIAGRAM LABELS: Fig. 1: VACUUM PASSAGE, FIG. 1 Fig. 2: VACUUM PASSAGE, HEAT TUBE, FIG. 2 Fig. 3: HOOK OF SPRING MUST REST AGAINST EAR, FAST IDLE LEVER AND CAM MUST MOVE FREELY, FAST IDLE ROD MUST NOT STICK OR BIND IN SLOT, FIG. 3 Page 2—Form 10C-638 | ||