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SECTION 5. OVERHEAD VALVE ENGINE CARBURETORS
Overhead valve engines utilize Walbro carburetors.
CARBURETOR ADJUSTMENT. Carburetor factory
adjustment should not be changed. However, if required,
perform the following: with engine running (Allow
engine to warm up for 5 minutes). Open throttle (speed
control at “RUN” or “FAST” position). Adjust high
speed adjustment screw per chart, clockwise or
counterclockwise until engine runs smoothly. With
control in idle or slow position, adjust idle speed
adjustment screw to obtain correct idle speed. If
necessary, readjust idle adjustment screw clockwise
or counterclockwise until engine idles smoothly.
HIGH SPEED
CARB. ADJ. SCREW* IDLE ADJ. SCREW*
OH120
THRU 1 TURN* 1 TURN*
OH180
*All Adjustments Off of Seat
IDLE ADJUSTMENT SCREW. Close idle adjustment
screw by turning clockwise. Close finger tight only.
Forcing will damage screw.
OPEN IDLE ADJUSTMENT SCREW: 1 turn
counterclockwise.
Start engine and with the throttle open (then return
to idle position), adjust idle adjust screw one-eighth
(1/8) turn at a time clockwise or counterclockwise
until engine runs smoothly.
With control at “idle” or “slow” position, adjust idle
speed adjustment screw to obtain correct idle speed.
If necessary, readjust idle adjustment screw until
engine idles smoothly.
CARBURETOR SERVICING
Throttle Shutter
Install the throttle shutter with the numbers facing
out when closed. Move the throttle shaft to the closed
position, place the throttle shutter on the shaft and
secure with new retaining screws. The throttle should
move freely. If binding is present, correct by loosening
screws and repositioning throttle shutter.
CHOKE SHUTTER. Position the choke shaft and
shutter in the closed position to tighten the screws.
Hard starting may be due to misaligned choke plate.
Correct by readjusting the plate to close completely.
HIGH SPEED ADJUSTING SCREW. Prior to removing
the fuel bowl nut, remove the high speed adjusting
needle. When replacing the fuel bowl nut be sure
to position a fiber gasket on each side of the fuel
bowl.
THROTTLE PLATE
CHOKE LEVER
CHOKE
SHUTTER
THROTTLE
RETURN SPRING
IDLE
ADJUSTMENT
SCREW
FUEL BOWL
FUEL BOWL
RETAINING NUT
HIGH SPEED
ADJUSTMENT SCREW
ATMOSPHERIC
VENT OPENING
IDLE SPEED
ADJUSTMENT
SCREW
THROTTLE PLATE
INSTALL WITH
NUMBERS OUT
IDLE SPEED
ADJUSTMENT
SCREW
RETAINING
SCREWS
THROTTLE
SHUTTER
MOUNTING
FLANGE
INSTALL WITH
NUMBERS OUT
ATMOSPHERIC
VENT
AIR CLEANING
MOUNTING
CHOKE SHAFT
CHOKE
SHUTTER
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