TM 55-4920-384-13&P
MARVEL-SCHEBLER CARBURETOR
FOR WISCONSIN MODEL MVG4D ENGINE
ADJUSTING CARBURETOR
DESCRIPTION
1. The Model VH-69-A (Wis. No. L-54-J-1) is a float
1. To start the engine, close the choker fly. When
type carburetor with idle fuel adjustment designed
the engine starts, open choker to the proper warm-
for use with the Model MVG4D Wisconsin Air
up position. After engine has warmed up, open
Cooled gasoline engine, and is made up of two
choker fully.
major unitsa die cast aluminum throttle body and
2. Close the throttle and adjust the throttle atop
a stamped steel fuel bowl.
screw to give the proper idle speed. The idle ad-
2. The model number is stamped on a square boss,
justing needle should be in proper adjustment at
provided for it on the body casting.
about 3/4 to 1 turn open, Turn the idle adjusting
needle open until engine rolls from "richness",
OPERATION
Then turn the needle towards the seat until the
engine runs irregularly from "leanness", From the
With the throttle fly slightly open from the closed
"lean" setting, open the idle adjusting needle to
position to permit idling, the main fuel nozzle may
the richest mixture that will not cause the engine
be delivering little or no fuel, as only a very small
to "roll" or run unevenly, This adjustment will,
quantity of air passes through the mixing chamber at
in most cases, give a slower idling speed than a
this time. An idle pasaage is provided to carry suffi-
slightly leaner adjustment with the same throttle
cient air and fuel to the engine side of the throttle
stop screw setting, but will give the smoothest
fly where the suction is high, This passage takes
idle operation. After the idle adjusting needle set-
the air from the inlet side of the venturi to the inter-
ting has been made, it may be necessary to revise
section of the vertical idle fuel passage (which con-
the throttle atop screw setting to give the proper
nects with the main nozzle assembly) and delivers
idling speed.
the air-fuel mixture through an opening controlled by
the idle adjusting needle to the throttle barrel just
beyond or on the engine side of the throttle fly. The
idle system is practically independent of the main
CAUTION:
nozzle system, and only controls the fuel metering
Care should be taken not to damage the idle adjust-
at low engine speed. As air-flow increases with the
ing needle nor its seat by turning the idle adjusting
opening of the throttle fly the main nozzle begins to
needle too tightly against the seat, as damage to
deliver fuel, and the delivery from the idle system
either of these parts will make a satisfactory idle
decreases until at full throttle, delivery is entirely
adjustment very difficult.
from the main nozzle.
MARVEL-SCHEBLER CARBURETOR DIVISION, BORG-WARNER CORPORATION
D E C A T U R , ILL., U.S.A.
D-79