FUEL SYSTEM
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
67. GENERAL.
=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.
=68. CARBURETOR ADJUSTMENT= (fig. 43).
=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.
[Illustration: RA PD 310240
_Figure 43—Throttle in Fully Closed Position_]
[Illustration: RA PD 310241
_Figure 44—Throttle in Fully Open Position_]
=69. THROTTLE CONTROL WIRE ADJUSTMENT= (figs. 43 and 44).
=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.
70. CARBURETOR REMOVAL.
=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 1/2-inch thick steel spacer fitted between carburetor and
manifold on some models._
(6) Remove carburetor.
(7) Remove fuel strainer assembly from carburetor bowl nipple.
71. CARBURETOR INSTALLATION
=a.= When installing carburetor be sure to fit the 1/2-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.
[Illustration: RA PD 310242
_Figure 45—Removing Fuel Strainer_]
(2) To install carburetor on manifold, locate carburetor flange and
two gaskets (1/2-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).
=72. FUEL STRAINER= (fig. 45).
=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.
73. CARBURETOR BOWL CLEANING.
=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.
74. FUEL PIPE.
=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.