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).
Service and adjustment instructions for a Stromberg carburetor automatic choke control.
| Identifier | ExFiles\Box 122\3\ scan0217 | |
| Date | 18th March 1940 guessed | |
| PACKARD 1903 1940 STROMBERG CARBURETORS 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 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 “B” is governed by the quantity of in-rushing 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 out of all 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. CHECKING FAST IDLE ADJUSTMENT—FIG. 4 To check the fast idle setting of the carburetor, it is merely necessary to hold the stop screw “E” on the high lobe of the fast idle cam as illustrated in FIG. 4. Move the choke valve as far as possible to the closed position. The opening in this position should be equivalent to a 3/32″ drill. If this amount of opening is not obtained, it is only necessary to slightly bend the fast idle rod at the point indicated in FIG. 4. Care should be taken so as to not to cause a bind in the fast idle mechanism. CHOKE RELEASE—FIG. 5 If for any reason the engine should become flooded, the choke valve can be partially opened by depressing the accelerator pedal to the full extent of its travel. This results in ear “G” of the throttle lever making contact with the fast idle loose lever, rotating it and forcing the choke valve partially open. With the throttle in the wide open position, the space between the top of the choke valve and the air horn should be between .156″ and .217″. This can be measured by placing a drill of 11/64″ diameter between the valve and the air horn. If it is necessary to readjust this, it can be done by bending ear “G” to the desired position. Tool T-25056 choke valve setting gauge is recommended instead of using drills. 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 operation 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. Disconnect the heat tube from the thermostat housing. 2. Remove carburetor from manifold. 3. Remove thermostat cover screws and lug washers. Thermostat cover assembly can then be taken off the choke housing. 4. Loosen locknut, removing lock washer and serrated washer. 5. Remove vacuum piston assembly from housing. 6. 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 thoroughly cleaned. Do not use any abrasive materials for cleaning piston or cylinder. 7. Thoroughly clean the screen on the inside of the housing compressed air into the heat tube connection, 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 on the choke lever. The indication mark 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 a No. 70 drill (.028) between the choke valve and the air horn as illustrated in Fig. 6. Tighten locknut lightly with tool T-25047. 4. Remove 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 best performance with the regular blends of gasoline. When placing the thermostat cover assembly on the housing, use precaution that the edge of the screen is not crimped or creased to cause a leak. Locate the thermostat hook at the bottom of the housing and then rotate the cover in the “RICH” direction until the “A” mark coincides with the projection on the housing. This procedure is recommended to make certain that the thermostat hook contacts the choke lever. Place the lugs in position and fasten the cover 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. A No. 3 is stamped on the thermostat cover for identification. NOTE: When assembling heat tube connection nut into thermostat cover, do not use excessive pressure in order to avoid changing the position of the cover. Page 2—Form 10C-639 Form 10C-639—Page 3 | ||