DESCRIPTION
The 1408 Series Carburetor is a horizontal "balanced" type with concentric fuel bowl, a single "doughnut"- shaped float fixed main jet, three-position, spring-loaded choke plate: an idle adjusting needle and throttle stop screw. The venturi is cast integral with the throttle body and the idle tube, main discharge tube and well vent tube are pressed permanently into an elongated boss on the throttle body. This boss serves as the mounting support for the fuel bowl, as well as the main jet. In the "balanced" type carburetor, all air for float chamber ventilation, well ventilation and for idle and main jet operation must enter through the air cleaner. In this design, any restriction in the air cleaner will have a minimum effect upon the fuel-air mixture admitted to the engine.

The FUEL SYSTEM controls the level of fuel in the float chamber (fuel bowl) at all times and under all conditions of operation. The Fuel Supply System consists of: the fuel inlet fitting, float chamber, fuel valve (needle and seat), doughnut-shaped float with double hinges, and a single float lever.

The IDLE SYSTEM supplies the fuel-air mixture for idle and off-idle (low part - throttle operation). The Idle System consists of: idle tube, idle air bleed, connecting channels, three idle discharge hole, idle adjusting needle and throttle plate.

The HIGH SPEED (main metering) SYSTEM supplies the fuel-air mixture for part throttle to full throttle operation. The High Speed System consists of: venturi, discharge nozzle, metering well and tube, well vent, main jet and connecting channels.

The CHOKE SYSTEM provides a richer mixture of fuel and air for starting a cold engine. The Choke System consists of: an external choke lever and detent spring, choke shaft and choke plate.

OPERATION

FUEL SUPPLY SYSTEM (Fig. 1)
Fuel under pressure is supplied to the carburetor through the fuel inlet, to the fuel valve (needle and seat), and on to the float chamber. With fuel in the float chamber, the float automatically regulates the opening through the fuel valve to maintain a specified level of fuel in the float chamber even though the fuel flow demands vary with engine speed and load.

IDLE SYSTEM (Fig. 2) The fuel for idle operation is drawn from the metering well through the idle tube calibration and mixed with air entering through the idle air bleed in the channel leading to the idle discharge holes. At low idle speed, the throttle plate is positioned so that only the #1 idle discharge hole is exposed to engine vacuum.. Since the #2 and #3 idle holes are exposed to the air entering the carburetor, air is adnutted through idle holes #2 and #3 to be mixed with the fuel-air mixture in idle channel before being discharged through the #1 idle discharge hole into the intake manifold. Opening the throttle plate slightly exposes the #2 idle discharge hole to engine vacuum to feed more fuel-air mixture into the engine. As the throttle is advanced slightly, the #3 idle discharge hole is also exposed to engine vacuum, increasing the fuel-air supply to the engine still further. At this throttle position, any further throttle advance brings the high speed system into operation. The idle adjusting needle regulates the fuel-air mixture flowing through the #1 idle discharge hole. Turning the idle needle valve IN (clockwise) results in a leaner mixture. Turning it OUT (counter-clockwise) provides a richer mixture. The idle speed is set by adjusting the throttle stop screw and not by the idle adjusting needle.

CHOKE SYSTEM (Fig. 2)
Before cranking the engine, the carburetor throttle should be opened just enough to expose all three idle discharge holes to engine vacuum. The choke should be held fully closed during cranking and opened slightly (one notch) shortly after the engine starts. As the engine warms up, the choke should be opened to the third notch, wide-open, and the throttle should be returned to the low idle position.

HIGH SPEED SYSTEM (Fig. 3)
Fuel for the off-idle to full throttle range of operation is supplied from the fuel bowl through the main metering jet to the discharge nozzle, where it is mixed with air taken in from the air intake in front of the venturi and with air drawn into the discharge nozzle from the chamber surrounding the venturi. This mixture of fuel and air then passes through the discharge nozzle into the air stream at the throat of the venturi. To insure the correct mixture ratio, a small amount of air is added from the well vent or high speed bleed, through the air bleed holes located in the wall of the metering well at various levels. By introducing air into the system below the fuel level in the fuel bowl, the surface tension of the fuel is reduced, enabling the fuel to flow at lower suction. At high suction, the air from the well vent proportionately reduces the flow of fuel to provide a correctly balanced mixture ratio at all engine speeds and loads.

DISASSEMBLY

REMOVAL OF FUEL BOWL
1. With carburetor inverted, loosen main jet (18). Remove main jet assembly, washer (19) and fuel bowl (12).
2. Inspect main jet (18) for wear.

DISASSEMBLY OF THROTTLE BODY
1. Stand throttle body (1) on end and use scribe or heavy wire to press float axle (10) out of float hinges. Remove axle and float (9). 2. Hold hand under fuel inlet and turn throttle body to horizontal position. Catch fuel valve, pin and spring (parts of 20) as they fall from seat.
3. Remove idle adjusting needle (5) and spring (6) by unscrewing them (counterclockwise). Remove throttle stop screw (7) and spring (8) in the same way.
4. Lay throttle body down with fuel bowl side up. Use large screwdriver to remove fuel valve seat (part of 20) and washer (21) from fuel inlet port.
5. Remove bowl to body gasket (11).
6. Close choke plate (16), and use small screwdriver to remove screws (17). Slide choke plate out air intake opening and choke shaft and lever (15) out shaft hole. Do NOT remove choke detent spring (24) unless it is damaged and must be replaced.
7. Close throttle plate (13), and use small screwdriver to remove screws (14). Slide throttle plate out manifold opening and throttle shaft and lever (23) out shaft hole. Use small screwdriver to pry seal retainer (3) and seal (2) off shaft hole boss. Do NOT remove shaft hole plugs (4) unless they are damaged and must be replaced.

SERVICE AND REPAIR PROCEDURE

IDENTIFY CARBURETOR
Check the numbers on the metal identification disc pinned to the top of the throttle body or indented in it. The plain number is the Zenith assembly number, the number with the letter "L" pre-fixed to it is the engine manufacturer's part number, for the complete assembly.

EXPLODED VIEW (Fig. 4)
The exploded view identifies the serviceable component parts of the carburetor and shows their relationship to the complete assembly. Use the key numbers on the exploded view to identify and locate parts when performing both the disassembly and assembly operations.

CLEANING
Thoroughly clean all metal parts in Bendix Metalclene or Speedclene and rinse in cleaning solvent. Blow out all passages in throttle body and fuel bowl with reduced air pressure. Be sure all carbon deposits have been removed from throttle bore and idle discharge holes. Reverse the flow of compressed air through all passages to insure the removal of all dirt. NEVER USE A DRILL OR WIRE TO CLEAN OUT JETS OR IDLE HOLES.

INSPECTION OF PARTS
1. Float Assembly - Replace if loaded with gasoline, damaged or if float axle bearing is worn excessively. Inspect float lever for wear at point of contact with fuel valve needle. Replace if wear is excessive.
2. Float Axle Replace if any wear has occurred on the bearing surface.
3. Fuel Valve (Needle & Seat) Assembly - Replace as a complete unit. Wear of any of these parts can seriously affect the operation of the float.
4. Idle Adjusting Needle -Inspect tapered end of the needle to make sure it is smooth and free of grooves. Replace if pitted or grooved.
5. Gaskets, Seal and Retainer - Replace all gaskets, throttle shaft seal and retainer each time the carburetor is overhauled.

REASSEMBLY

ASSEMBLY OF THROTTLE BODY
1. Slide throttle shaft and lever (23) into seal retainer (3) and seal(2). Insert shaft into throttle shaft hole at manifold end of throttle body (1). Seat shaft in hole on opposite side of throttle bore and press seal and retainer firmly against shaft hole boss.

2. Rotate throttle lever so flat center section faces out manifold opening. Install throttle plate (13) with screws (14), using small screwdriver.

3. Slide choke shaft and lever (15) into choke shaft hole and seat in hole on opposite side of air intake bore.

4. Rotate choke shaft so flat center section faces out intake opening. Install choke plate (16) with screws (17), using small screwdriver.

5. Lay throttle body down with fuel bowl side up and in stall bowl to body gasket (11).

6. Install washer (21) and fuel valve seat (part of 20). Use large screwdriver to tighten seat to 100 in-lbs. Insert valve, spring and 'pin (parts of 20) into seat.

7. Install float (9) and float axle (10) on support brackets of throttle body. Check operation of the float to be sure the hinge and axle do not bind and that the float moves in a perpendicular direction.

8. Install throttle stop screw (7) and spring (8). Adjust screw to open throttle slightly but not far enough to uncover #2 idle discharge hole, see Fig. 2.

9. Install idle adjusting needle (5) and spring (6). Screw needle IN (clockwise) until it seats lightly against the #1 idle discharge hole, then back it out 1 1/2 turns as a preliminary idle adjustment.

FLOAT SETTING

1. With fuel bowl removed, set depth gauge to dimension recommended in illustration, Fig. 5.

2. Hold throttle body assembly in an inverted position and at the same time, support float so that tab or float lever just contacts fuel needle valve without any pressure or weight.

3. Place depth gauge in position as illustrated in Fig. 5.

4. CHANGING FLOAT LEVEL POSITION
If float position is not to the dimension shown by depth gauge, remove float and bend tab (or lever) that contacts the needle pin (use long-nose pliers - close to the float body), until correct dimension is obtained. Reassemble float to throttle body and recheck float level position.