Mercury 305 CID, Service Manual, Page: 526 / 967

5D-28 - WEBER 4 BARREL CARBURETOR 90-823225--1 1096
30. Remove mixture screws.
70467
b
a
a - Idle Mixture Screw
b - Spring, Idle Mixture Screw
Cleaning and Inspection
! CAUTION
Rubber, plastic parts, pump plungers or dia-
phragms cannot be immersed in carburetor
cleaner.
! CAUTION
Avoid damage to carburetor. Do not leave carbu-
retor in immersion-type cleaner for more than
two hours.
IMPORTANT: Do not immerse metering rod
springs in carburetor cleaner; the color, if not
“natural” metal, may be removed. Clean
separately as needed.
1. Clean metal carburetor parts in a commercial, im-
mersion-type cleaner, until all deposits have
been removed. Follow manufacturer’s instruc-
tions of cleaner being used for proper cleaning
and rinsing procedures.
! CAUTION
Avoid personal injury. Always wear safety
glasses when using compressed air.
2. Blow out passages with compressed air. Do not
drill through passages.
IMPORTANT: DO NOT use a wire or drill to clean
jets, passages, or tubes in carburetor, as this
may enlarge orifices and seriously affect carbu-
retor calibration.
3. Wipe all parts that cannot be cleaned in immer-
sion cleaner with a clean, dry cloth.
4. Carefully inspect all carburetor parts for damage
or wear; pay particular attention to the following:
a. Idle mixture screws - Replace if damaged or
worn.
b. Fuel inlet needle valve and seat - Replace
with new needle and seat if worn or damaged.
c. Casting surfaces - Inspect accelerator
pump plunger well for scoring or deposits.
Replace worn or corroded components.
d. All linkage rods and levers - Replace if
worn or damaged.
e. Accelerator pump and plunger parts - Re-
place pump and parts if worn or damaged.
f. Float assembly and hinge pin - Float weight
of each should be the same. Replace either
if fuel can be heard inside when shaken.
Check hinge pin and holes for wear. Replace
components if worn or defective.
g. Throttle valves and shafts - Check for bind-
ing (through entire operating range, making
sure valves open and close completely) or for
looseness in carburetor body.
IMPORTANT: DO NOT remove throttle valves. If
any of the throttle parts or float bowl/carburetor
body shaft bores are found to be worn or dam-
aged, carburetor replacement is required.
h. Choke valve and shaft/lever assembly -
Check shaft and lever for excessive loose-
ness in air horn. Check choke valve and
shaft/lever assembly for binding through en-
tire operating range. Air horn assembly must
be replaced if choke valve and shaft/lever are
worn.
5. Check that choke pull-off diaphragm plunger re-
tracts when vacuum is applied to unit, and that it
holds vacuum (plunger remains seated if vacuum
is maintained).