Mercury 305 CID, Service Manual, Page: 457 / 967

5B-18 - MERCARB 2 BARREL CARBURETOR 90-823225--1 1096
1. Thoroughly clean all metal parts in a commercial
carburetor cleaner, until all deposits have been
removed. Follow cleaner manufacturer’s instruc-
tions for proper cleaning and rinsing procedure.
Dry parts with compressed air.
2. Using compressed air, blow out all passages in
carburetor to remove any foreign material.
3. Wipe off all parts that cannot be cleaned in carbu-
retor cleaner with a clean, dry cloth.
4. Carefully inspect all carburetor parts for wear and
damage; pay particular attention to the following:
a. Float Needle and Seat: If float needle or seat
is worn or damaged, replace with new needle
and seat assembly.
IMPORTANT: Float needle and seat are factory
matched and tested and should be replaced as a
set only.
b. Float Assembly and Hinge Pin: Check float
density (to see if it is saturated with fuel) by
comparing weight of float with specifications.
If weight is high, float assembly must be re-
placed. Check hinge pin and holes for wear.
c. Fuel and Air Passages: Passages must be
perfectly clean for proper carburetor opera-
tion.
d. Accelerator Pump Plunger and Return
Spring: Inspect pump plunger cup, pump
plunger spring (on pump assembly) and re-
turn spring.
e. Power Piston Spring: Check power piston
spring for weakness or distortion.
f. Idle Mixture Needle: Inspect idle mixture
needle. If damaged, needle must be re-
placed.
g. Levers and Linkages: Check levers, links
and rods for wear.
h. Throttle Valve and Shaft: Check throttle
shaft for excessive looseness in throttle body.
Check throttle valve and shaft for binding
through entire operating range, making sure
valve opens and closes completely. Throttle
body assembly must be replaced if throttle
valve and shaft are worn or damaged.
i. Choke Valve and Shaft and Lever Assem-
bly: Check shaft and lever assembly for ex-
cessive looseness in air horn assembly.
Check choke valve and shaft and lever as-
sembly for binding through entire operating
range, making sure valve opens and closes
completely. Air horn assembly must be re-
placed if choke valve and shaft and lever as-
sembly are worn or damaged.
j. Inspect Casting for visible damage. Inspect
gasket surfaces. Inspect accelerator pump
plunger well for scoring or deposits.
Reassembly
THROTTLE BODY ASSEMBLY
IMPORTANT: DO NOT force idle mixture needle
against seat as damage to needle and/or seat will
result.
1. Screw idle mixture needle (and spring) into
throttle body until they lightly seat, then back out
needle 1-1/4 turns as a preliminary idle mixture
setting. Final adjustment will be made with en-
gine running. Refer to “Adjustments.”
72293
b
a
a - Idle Mixing Adjusting Needle
b - Spring
2. Thread idle speed adjustment screw and spring
into throttle lever.
72395
b
a
a - Idle Speed Screw
b - Spring