Service and operation guide for the Stromberg Carburetor's automatic choke control.
| Identifier | ExFiles\Box 122\3\ scan0210 | |
| Date | 1st January 1940 | |
| BUICK 1940 STROMBERG 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. STARTING ENGINE For starting an engine that is cold enough to require full closing of the choke valve, additional tension takes place in the throttle hook-up after the accelerator pedal engages the starter. When starting the engine, the accelerator pedal should be depressed only to the point where the additional tension is noticeable. Moving pedal beyond this point will have a tendency to partially open the choke valve to admit sufficient air to clear manifold if the engine should have become flooded. OPERATION AND ADJUSTMENTS CHOKE CLOSED—FAST IDLE—COLD ENGINE When the engine becomes cold, the thermostat also cools and gradually gains sufficient tension to partially close the choke valve “A. {Mr Adams} ” As soon as the accelerator pedal is depressed to start the engine, the throttle is partially opened so that the throttle stop screw “E” is lifted away from fast idle cam “D. {John DeLooze - Company Secretary} ” This permits 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 after the engine is running, providing the proper throttle opening for the prevailing engine temperature. FIG. 1 shows the position of the choke and fast idle mechanism during the cranking period. The choke valve “A” is held in closed position during this operation by the tension of the thermostat “B.” CHOKE PARTIALLY OPENED—ENGINE RUNNING—WARMING UP PERIOD When the engine begins to fire, the manifold vacuum thus created pulls the vacuum piston “C,” opening the choke valve against the tension of the thermostat spring “B.” Sufficient air is thereby admitted to give a satisfactory running mixture. As the choke valve opening is increased, the fast idle cam is allowed to revolve so that the throttle stop screw comes to rest on a lower step when the throttle is opened and then permitted to close. FIG. 2. ENGINE WARM—CHOKE WIDE OPEN—SLOW IDLE While the engine continues to run, the inrushing air forces the off center choke valve “A” open. The amount the choke valve opens is controlled by the vacuum piston and tension of the thermostat. Heat is transmitted into the thermostat chamber by hot air being drawn from a “stove” in the exhaust manifold. The thermostat gradually absorbs sufficient heat so that its tension decreases until it does not offer any further resistance to the choke valve opening, and at the same time the fast idle cam “D” rotates until the throttle stop screw is at normal idle position. See FIG. 3. The throttle stop screw should be adjusted for a car speed of 7 to 8 M.P.H. at normal operating temperature. NOTE: The torsional spring of the fast idle cam has one end connected to the fast idle rod. Make certain that the washer is placed on the rod after the rod is assembled in the cam and that the hook of the spring is properly assembled on the rod. It is very essential that the cam moves freely and that the rod does not stick or bind in the slot of the cam. When checking the “START AID” mechanism, the fast idle cam setting is automatically obtained. The procedure is to hold a No. 53 drill between the choke valve and the air horn as illustrated in FIG. 4. In this position, locking lever “J” should just clear loose lever “H” while the throttle is opened and closed. To obtain the desired clearance, bend the fast idle rod at the point indicated. Care should be taken so as not to distort the fast idle cam return spring or cause a bind between the rod and the slot in the cam. With the throttle in the wide open position, the space between the top of the valve and the air horn should be between .156” and .187”. This can be measured by placing a drill of 11/64” diameter between the valve and the air horn, FIG. 5. This setting is properly made at the factory; however, if it is necessary to re-adjust, it can be done by bending ear “P” to the desired position. Care should be taken to make certain that the fast idle rod does not bind and the fast idle cam spring is not distorted. SERVICING THE AUTOMATIC CHOKE CONTROL The automatic choke control is properly set at the factory. Under ordinary circumstances it will give many miles of satisfactory service. In the operations of an automatic choke control the one point that must be borne in mind at all times is that all parts of the unit must operate freely and not stick or bind in any position of travel. DISASSEMBLY 1. Remove carburetor from manifold. 2. Remove thermostat cover screws and lug washers. Thermostat cover assembly can then be taken off of the choke housing. 3. Loosen lock nut, removing lock washer and serrated washer. 4. Remove vacuum piston assembly from housing. 5. With a clean rag saturated with acetone or alcohol, thoroughly clean the cylinder walls of any dirt or other foreign material which may have accumulated in regular service. Use compressed air to blow out all of the channels. The surface of the piston should also be cleaned. Do not use any abrasive materials for cleaning piston or cylinder. 6. Thoroughly clean the screen on the inside of the housing and the screen on the inside of the cover by blowing compressed air into the heat tube connection, and also between the screen and the cover, using precaution not to distort the screen. REASSEMBLY 1. Place vacuum piston in cylinder with slot on piston assembled down. THIS IS VERY IMPORTANT. ALSO DO NOT USE ANY TYPE OF LUBRICANT ON PISTON OR IN CYLINDER. Assemble lever onto choke stem. Next assemble serrated washer, lockwasher, and locknut, fastening the nut merely by hand. 2. Referring to FIG. 6, place tool T-25046 on choke housing with the small hole (H) fitting over the pin of the choke lever. The indication line at the outer diameter of the tool should be set to line up with the projection on the choke housing. The tool should be held in this position by hand or two of the cover screws and lug washers can be used to do this. 3. Holding choke valve against 15/64” drill for AAV-16, or a No. 3 drill for AAV-26, between the choke valve and the air horn as illustrated in FIG. 5, tighten locknut lightly with tool T-25057. 4. Remove tool T-25057 and tool T-25046. Hold choke valve in closed position and tighten locknut securely. CHECK CHOKE VALVE OPENING to be certain the setting wasn’t disturbed. Do not endeavor to change position of serrated washer or piston lever without loosening locknut. THERMOSTAT SETTING The thermostat is calibrated and properly set at the factory to give satisfactory performance with the regular blends of gasoline. When placing the thermostat cover assembly on the housing, use care that the edge of the screen is not crimped or creased to leak. Locate the thermostat hook at the bottom of the housing and then rotate the cover in the “RICH” direction until the “O” mark coincides with the projection on the housing. This procedure is followed to make certain that the thermostat hook contacts the pin on the choke lever. Place the lugs in position and fasten the cover screws securely. If extremely high volatile fuel is continuously used or if some exceptional condition is encountered, it may be desirable to slightly vary the adjustment of the cover to obtain the best possible performance. Do not, however, vary the adjustment more than two graduations in either direction. The thermostat need not be changed unless some part of the assembly has been tampered with or is damaged. In such cases it is necessary to replace the entire assembly. The numeral “6” is stamped on the face of the thermostat cover to distinguish them from covers used on previous models. NOTE: When assembling heat tube connection nut onto thermostat cover do not use excessive pressure in order to avoid changing the position of the cover. Diagram Labels: Fig. 1: VACUUM PASSAGE, A, B, C, D, E Fig. 2: VACUUM PASSAGE, HEAT TUBE, A, B, C, D Fig. 3: CAM & LOOSE LEVER MUST MOVE FREELY, FAST IDLE ROD MUST NOT STICK IN SLOT, A, B, C, D, E Fig. 4: NO. 53 DRILL (.0595"), BEND ROD "D" TO OBTAIN THE DESIRED CLEARANCE AT POINT "K" BETWEEN "H" AND LOCKING LEVER "J", LOCKING LEVER "J", LOOSE LEVER "H", CLEARANCE Fig. 5: 11/64" DIA., BEND EAR "P" TO OBTAIN PROPER CHOKE VALVE AT OPEN Fig. 6: T-25046 VACUUM PISTON SETTING GAUGE, T-25057 SOCKET WRENCH FOR LOCKNUT, NOTE: 15/64 DRILL FOR AAV-16 SERIES. NO. 3 DRILL FOR AAV-26 SERIES, 60, 70, 80, 90. COVER SCREWS, LUG WASHERS, VACUUM PISTON ASSEMBLY, SLOT, SERRATED WASHER, LOCKWASHER, LOCKNUT, THERMOSTAT COVER ASSEMBLY, "A" MARK TO CONCIDE WITH INDICATOR ON HOUSING, WHEN FASTENING HEAT TUBE CONNECTION DO NOT USE EXCESSIVE PRESSURE IN ORDER TO AVOID CHANGING POSITION OF THERMOSTAT COVER, INDICATOR MARK, INDICATOR SLOT, "H", VACUUM PISTON, SLOT. Footer: Page 2—Form 10C-636 Form 10C-636—Page 3 | ||
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).