The following information from a Repair Manual for Star Cars was sent to us by Bob Krause, Long Beach, California. Bob said "if you understand how your carburetor and vacuum tank work; you will be able to handle any problem.
As the gasoline tank is mounted on the rear of the car, some distance from the carburetor, it is necessary to provide a means of drawing the fuel from the tank into the carburetor. This is accomplished by the use of a vacuum tank mounted under the hood, the construction of which is illustrated in Fig. 56. Every motor draws its supply of gasoline through the carburetor by reason of the pumping action of the pistons, which, on their downward or suction stroke, create a partial vacuum in the intake pipe. Care and Repair of Vacuum System before proceeding to repair the vacuum tank, make absolutely sure that the trouble is not due to some other cause.
Vent Tube Overflows
The air vent, 12, allows an atmospheric condition to be maintained in the lower chamber, and also serves to prevent an overflow of gasoline in descending steep grades. If once in a long while a small amount of gasoline escapes no harm will be done, and no adjustment is needed. However, if the vent tube regularly overflows, the air hole in main gasoline tank filler cap may be too small, or may be stopped up. If the hole is too small, or if there is no hole at all, the system will not work. Enlarge hole to Y8" diameter, or clean it out.
Remember that this condition may be due to other causes than the vacuum system. Do not blame the vacuum system until you are sure that the fault does not lie elsewhere. After flooding the carburetor, or "tickling the carburetor," as it is commonly called, if gasoline runs out of the carburetor float chamber you may be sure that the vacuum is performing its work of feeding the gasoline to carburetor.
Another test is to take out the inner vacuum tank, leaving only the outer shell. If you fill this shell with gasoline and the motor still refuses to run properly, then the fault clearly lies elsewhere, and not with the vacuum system-because you must certainly get gasoline feed from this open, elevated tank of gasoline, unless there is stoppage in the connection line to carburetor.
To Remove Top
In removing top of tank, after taking out screws, run the blade of a knife carefully around top, between cover and body of tank, so as to separate gasket without damaging it. Gasket is shellacked to make an airtight joint. If Faulty Feed Is Traced to Vacuum System, One of the Following Conditions May Be the Cause:
(A) The float, which should be air-tight, may have developed a leak, thus filling up float with gasoline and making it too heavy to rise sufficiently to close vacuum valve. This allows gasoline to be drawn into manifold, which in turn will choke down the motor. Proper operation depends upon the float being airtight.
To Repair Float
Remove top of tank (to which float is attached) as above directed. Dip the float into a pan of hot water, in order to find out definitely where the leak is. Bubbles will be seen at point where leak occurs. Mark this spot.
Next, punch two holes, one in the top and the other in the bottom of the float, to permit discharge of the gasoline. Then solder up these holes and the leak. Test the float by dipping in hot water. If no bubbles are seen, the float is airtight. In soldering float, be careful not to use more solder than required. Any unnecessary amount of solder will make the float too heavy. In taking out float and repairing it, take care not to bend the float guide rod. If you bend the rod, it will strike against guide and retard float, producing the same effect as a leaky float, and allowing gasoline to enter manifold. Also note whether surface of rod is perfectly smooth, so that it cannot be retarded by guide.
To overcome the condition of a leaky float temporarily until you can reach a garage, remove plug 15 at the top. In some cases the suction of the motor is sufficient to draw gasoline into tank even with this plug open, but not enough to continue to be drawn into manifold. If, however, you are not able to do this, close up plug, 15, with engine running. This will fill tank. After running engine until tank is full, remove plug, 15, until gasoline gives out. Repeat the same operations until a repair station or garage is reached, where the leaky float can be remedied.
(B.) The flapper valve, 6, may be out of commission. A small particle of dirt getting under the flapper valve might prevent it from seating absolutely airtight, and thereby render the tank inoperative. In order to determine whether or not the flapper valve is not functioning, first plug up air vent; then detach tubing from bottom of tank to carburetor. Start motor and apply finger to this opening. If suction is felt continuously, then it is evident that there is a leak in the connection between the tank and the main gasoline supply, or else the flapper valve is being held off its seat and is letting air into the tank instead of drawing gasoline. In many cases this troublesome condition of the flapper valve can be remedied by merely tapping the side of the tank, thus shaking loose the particle of dirt or lint which has clogged the valve, If this does not prove effective, remove tank cover, as described on previous page. Then lift out the inner tank. The flapper valve will be found screwed into the bottom of this inner tank.
(C.) Manifold connection, 3, may be loose, allowing air to be drawn into manifold.
(D.) Tubing may have become stopped up in lengths 4 or 3.
(E.) Gasoline strainer, 5, is a screen located in the line from gasoline tank. This screen collects all foreign substances that might get in the rear tank and be carried through to the carburetor, and clog it. If tank fails to work it may be that this screen is clogged, preventing gasoline from getting into tank. Screen may be easily cleaned by unfastening connection at elbow. This cleaning should be done every three weeks. If tank should ever fail to operate, examine strainer first.
The Tillotson Carburetor is especially designed for the STAR engine. It is a plain tube carburetor with air-feed main nozzle, accelerating well, and a bypass for idling. The upper cross-holes in main nozzle feed air above the level of gasoline and thin out the mixture at ordinary speeds to give maximum economy. The lower cross holes fill the accelerating well, and empty it when throttle is opened quickly. The needle valve regulates the flow of fuel to main nozzle. The approximate setting is two and one-fourth turns open. To adjust, open throttle one-third, retard spark, adjust needle valve until engine runs smoothly, then cut off one-eighth to one-fourth turn, which should give you best performance.
The by-pass needle regulates the air for idling, the approximate setting is one-fourth to one-half turn open. The position of butterfly to give required speed is determined by a stop screw, which should be adjusted at the same time as the by-pass needle. When desired speed is secured, lock the screw by binder screw. Before adjusting carburetor, spark plugs, and ignition system and valves should be in good order; gasoline line and strainers free and clean, and engine well warmed up. A large proportion of carburetor trouble is due to water or dirt in gasoline stopping up the screen and nozzles.
This instrument has been designed and adjusted for use with gasoline fuel; when using other fuels, secure instructions from Tillotson Mfg. Co., or authorized service stations. The carburetor has been carefully tested and properly adjusted with motor at the factory, and no further adjustments should be necessary. often attempts are made to adjust the carburetor when something is causing the motor to run unevenly. The carburetor is equipped with a filtering screen or strainer at the point where the gasoline enters the carburetor. Dirt or water may be causing the motor to misfire and sputter; and in this event, the bowl to which the gasoline line is connected should be removed and thoroughly cleaned.
If dirt should pass the screen or strainer, it may lodge so that needle valve will not have a good seating. In this event, it would cause a leaky carburetor, and the needle valve should be reseated. Remove the cover over the float chamber bowl and with a light hammer other suitable tool, tap lightly on the end of the needle valve. The needle valve seat is made of brass and this action will cause a new t to be formed. A slight drip from the carburetor is sometimes due to the gasoline level being too high. The lever for this carburetor is 13/16" from the of the float chamber to the surface of the gasoline. The level can be changed by bending the float lever arms. In nearly every case of difficulties encountered with a carburetor, you will find that dirt in the carburetor or passages between the gasoline tank and carburetor is a contributing cause.
TO CLEAN CARBURETOR
Disassemble the carburetor completely and examine each part. Clean all parts thoroughly in gasoline using a stiff brush to remove caked dirt and blow out the small drilled passages which may become clogged with chips or dirt. Inspect carefully for defects in fiber washers or leaks due to sand in body castings. If due care is exercised, further difficulties can generally be traced to insufficient fuel feed, faulty ignition or poor compression.