II CARBURETOR ADJUSTMENT - Both the idle mixture adjusting screw and the main
jet adjusting screw are for adjusting fuel/air mixture. Turning either screw
clockwise (closing jet) will reduce the amount of fuel being mixed with the air
causing the mixture to become leaner. Turning either screw counterclockwise
(opening jet) will increase the amount of fuel being mixed with the air, and the
mixture becomes richer. Basically, the idle mixture screw affects the mixture at
idle RPM, and the main jet adjusting screw affects the mixture at cruising.
speeds and above. At speeds between idle and cruise, both jets may be partly
active, varying with the throttle setting.
IF THE ENGINE does not smoke, idles smoothly and quietly accelerates without
stalling, and cruises with steady power, the carburetor needs no further
adjustment.
ASSUMING THAT there are no other problems such as an air leak under the
carburetor or adapter1 or ignition trouble), yet the engine still runs rough and
possibly smokes ~lack) heavily1 then the mixture is to rich. If the engine pops
or backfires thru the carburetor, or hesitates during acceleration, the mixture
is too lean. In either case, the engine will not deliver full power.
IF THE MIXTURE is too lean, an engine may not start for lack of fuel; if too
rich, an engine may not start because it becomes flooded.
FOR ANY OF THE ABOVE DIFFICULTIES, ADJUST THE CARBURETOR As FOLLOWS~
(a) Close the idle mixture and main jet adjusting screws, turning them in a
clockwise direction.
CAUTION: Carefully turn the screws only until they can be felt to have
touched their seats. Too much pressure can change the shape of their needle
points and the jets, making proper adjustment difficult or even impossible.
(b)
If the engine has been flooded, open the throttle and the choke. Pull thru
several times with the starter to clean out the excess charge.
Cc) Open the idle mixture and main jet adjusting screws 1.5 turns
counter-clockwise for initial settings.
Cd) Start the engine as instructed under OPERATING PROCEDURES.
Ce) With the engines warm and the choke open, adjust idle speed to the
desired RPM.
Cf) Alternately adjust the idle mixture screw until the engine idles smoothly
at the speed required by the specific installation.
Cg) Adjust the main jet adjusting screw so the engine, when under load, will
accelerate without hesitation, and will run smoothly without excessive smoking
at all speeds up to the maximum safe RPM. This may require some re-adjustment of
the idle mixture and the idle speed screw. After final adjustment, the minimum
setting for the idle mixture screw is 3/4 of a turn open, and 1 Cone) turn for
the main jet screw.
