| Paragraph | |
|---|---|
| General | 67 |
| Carburetor adjustment | 68 |
| Throttle control wire adjustment | 69 |
| Carburetor removal | 70 |
| Carburetor installation | 71 |
| Fuel strainer | 72 |
| Carburetor bowl cleaning | 73 |
| Fuel pipe | 74 |
a. Carburetor is of the side‐outlet, plain‐tube type with a fixed venturi. Fuel feed is by gravity from tank above. Carburetor has two manual controls: the throttle, which is operated by the right handle bar grip, and the choke, which is operated by a lever on the carburetor itself. The high speed fuel supply is governed by a fixed (non‐adjustable) jet. The idling to medium speed (30 mph) fuel supply is governed by an adjustable (low speed) needle valve located on rear side of carburetor body.
a. Before attempting to adjust carburetor to correct faulty engine performance, attention should be given other items which have a direct bearing on and can affect carburetor adjustment as well as engine performance.
(1) Inspect fuel tank cap and make sure air vent is not plugged.
(2) See that throttle control adjustment is correct (par. 69).
(3) See that spark control adjustment is correct (par. 88).
(4) Drain and flush carburetor bowl (par. 73).
(5) Drain and flush fuel strainer (par. 72).
(6) Inspect air cleaner to see that passage of air through cleaner is not restricted by oil level being too high in oil cup, or by an excessive accumulation of dirt in filter elements (par. 76).
(7) Check manifold packing nuts and carburetor mounting screws for tightness.
(8) See that spark plugs are clean and that gaps are adjusted between 0.025 inch to 0.030 inch. If condition of spark plugs is questionable, install new ones.
(9) Check adjustment of valve tappets (par. 43).
(10) Check compression of both cylinders (par. 29 b.) (1)
(11) Check condition and adjustment of circuit breaker points (par. 84).
(12) Check ignition to battery wiring connections (diagram fig. 48).
(13) See that battery is not entirely discharged by turning on lights (tactical situation permitting) and observing brilliancy.
b. A carburetor, once correctly adjusted, should require little, if any, readjusting. At most, it should not be necessary to adjust the low speed needle more than one or two notches either way to correct mixture to meet changes in weather conditions.
c. Low Speed Adjusting Needle (figs. 43 and 44). Adjustment of this needle valve controls only idling and low speed (up to approximately 30 mph) fuel mixture. Turn needle valve down (to right) to make mixture leaner. Back out (to left) needle valve to make mixture richer. Needle valve is held in any desired position by a spring‐and‐ball plunger which engages notches in the needle adjusting screw.
d. Complete Readjustment of Carburetor. A carburetor that is badly out of adjustment, and/or a new carburetor just installed, must be adjusted as follows:
(1) Turn the low speed needle valve all the way down (to right).
(2) Back needle valve out (to left) about three full turns. With needle valve in this position, engine will start, but mixture will probably be too rich.
(3) Start engine as follows: After choke lever has been moved to normal open running position and engine is normally hot, correct adjustment of needle valve by turning needle valve down (to right) one notch at a time until mixture becomes so lean that engine misses, and is inclined to stop: then back out (to left) needle valve 5 to 10 notches, or until engine fires regularly with spark advanced and throttle closed (or as nearly closed as it can be set and still have engine running at idling speed).
(4) Adjust throttle lever stop screw (fig. 43) as necessary to make engine idle at proper speed with throttle in fully closed position. Turning stop screw to the right makes engine idle faster. Turning stop screw to the left makes engine idle slower. Do not idle engine at the slowest possible speed, because an extremely slow idling adjustment causes hard engine starting. Changing idling speed with throttle stop screw is likely to change the low speed fuel mixture to some extent: therefore, it will be necessary to again check and correct the low speed needle valve adjustment (step (3) above).
(5) Engine starting and all‐round carburetion will be improved with low speed fuel adjustment slightly rich, rather than extremely lean.
a. Carburetor throttle is opened and closed by means of the right handle bar grip, operating a control wire (within a housing) which connects to the throttle lever. Adjustment for full opening and closing of the throttle to correspond with full inward and outward motion of the handle bar grip is made at the junction of the control wire end and the throttle lever connection.
b. Adjust Fully Closed Throttle (fig. 43). See that there is about 1 inch distance between end of control wire housing and throttle lever when in fully closed position, so that housing end does not interfere with forward movement of throttle lever. If adjustment of control wire housing is necessary, refer to paragraph 101. Proceed with closed throttle adjustment.
(1) Loosen control wire clamp screw in connector block.
(2) Turn right handle bar grip outward as far as it will go: then turn it inward slightly. Holding throttle grip in this position, move throttle lever forward against its stop (closed position) and secure control wire in connector block with clamp screw. Check closing of throttle after tightening control wire set screw. If necessary, reset the control wire in the connector block until throttle is closed with full outward grip movement.
c. Adjust Fully Open Throttle (fig. 44). Follow instructions under step b above, then:
(1) Turn right handle bar grip inward as far as it will go and see that throttle lever is against its stop in fully open position. If throttle does not open fully when grip is turned inward, reset the control wire in the connector block to correct the adjustment.
a. Remove Carburetor for Replacement Only.
(1) Shut off fuel supply valve.
(2) Loosen connector block clamp screw and disconnect throttle control wire at throttle lever.
(3) Disconnect fuel feed pipe at strainer nipple.
(4) Loosen air cleaner hose clamp at carburetor air intake fitting, and remove four screws and air intake fitting from carburetor.
(5) Remove the three mounting bolts (from right side of vehicle) which secure carburetor to manifold flange. CAUTION: Take care not to damage or lose gaskets found between carburetor flange and manifold flange, and/or ½–inch thick steel spacer fitted between carburetor and manifold on some models.
(6) Remove carburetor.
(7) Remove fuel strainer assembly from carburetor bowl nipple.
a. When installing carburetor be sure to fit the ½–inch thick steel spacer (if one was originally fitted) between carburetor and manifold flanges, with two gaskets on one side and one gasket on the other side. Later models have a longer manifold neck, extending carburetor farther to the left, away from cylinders, and do not need the spacer.
(1) Install fuel strainer assembly on bowl nipple. Leave coupling nut loose until after fuel pipe is connected.
(2) To install carburetor on manifold, locate carburetor flange and two gaskets (½–inch steel spacer and gaskets if originally fitted) to aline with holes in manifold flange, and insert and securely tighten the three carburetor mounting screws. Use a 7⁄16–inch socket wrench, or a large screwdriver, to securely tighten these screws. NOTE: If carburetor manifold is loose in manifold packing nuts (carburetor can be lifted and manifold turns in packing nuts), tighten manifold nuts securely, using manifold wrench (41–W–1570–10).
(3) Insert carburetor air intake fitting into end of air hose and mount fitting on carburetor with the four screws. Tighten air hose clamp.
(4) Connect fuel pipe to fuel strainer nipple by tightening the union nut and also the strainer union nut on bowl nipple.
(5) Attach throttle control wire to throttle lever connector block and adjust (par. 69).
(6) Open fuel supply valve and observe for leaks.
(7) Adjust carburetor (par. 68).
a. Cleaning.
(1) Shut off fuel supply valve.
(2) Unscrew cap from bottom of strainer body.
(3) Lift strainer screen element with cork washer out of cap and clean thoroughly. Remove any dirt or sediment collected in cap. NOTE: If compressed air is not available for cleaning, gasoline from the fuel pipe can be used for cleaning screen and cap.
(4) Install one cork washer in bottom of cap, set strainer screen element in place, and locate the other cork washer over screen element. Turn cap with screen element and washers onto bottom of strainer body, handtight.
b. Remove Strainer Assembly.
(1) Shut off fuel supply valve.
(2) Disconnect fuel feed pipe at strainer body nipple.
(3) Remove filter assembly from carburetor bowl nipple. It will be noted that coupling nut is an integral part of the filter body assembly.
c. Install Strainer Assembly.
(1) Install fuel strainer assembly on carburetor bowl nipple. Leave coupling nut loose until after fuel pipe is connected.
(2) Connect fuel pipe to strainer body nipple and tighten union nut. Strainer coupling nut can now be tightened on bowl nipple.
(3) Open fuel supply valve. Inspect fuel pipe and coupling nuts for leaks.
a. Water from fuel, water moisture, and dirt entering air cleaner will settle in bottom of carburetor bowl and will interfere with engine starting and carburetion. At periodic intervals bowl must be drained. NOTE: Before draining and flushing bowl, clean fuel strainer (par. 72).
(1) Support vehicle on jiffy (side) stand.
(2) Shut off fuel supply valve.
(3) Remove bowl drain screw. Let fuel, water, and dirt run out of bowl. With drain screw still removed, open fuel supply valve (turn to left) and leave open only a few seconds, to allow fresh gasoline to flush out bowl.
(4) Replace bowl drain screw, taking care to avoid thread crossing. Set screw snug, but not tight enough to strip the threads.
a. Remove.
(1) Shut off fuel supply valve.
(2) Remove pipe union nut from tank nipple. Remove pipe after disconnecting union nut from fuel strainer body nipple.
b. Install. Fuel pipe must be installed without putting undue twist or strain on pipe or end fittings. Therefore, bend and/or shape pipe to “fit” between nipple connections before replacing and drawing up on union nuts.
(1) Connect lower end of pipe to fuel filter body nipple. Do not tighten nut.
(2) Connect upper end of pipe to tank nipple. Securely tighten this nut. Next, tighten union nut on strainer body nipple.