Important Service Information; Point Carburetor Check List; Flooding At Idle Rpm - MerCruiser 305 CID (5.0L) Service Manual

SERVICE MANUAL NUMBER 24

Important Service Information

8 Point Carburetor Check List

To ensure that the carburetor is the cause of the problem, make the following checks BEFORE ordering
and installing a new carburetor. If questions 1, 2, 3, 5, 6 and 7 are YES and 8 is NO, the carburetor may
not be the problem.
1. Does the choke close completely before starting?
2. Does the choke open completely during engine warm-up?
3. Is idle mixture screw set correctly?
(Engines with Thunderbolt V ignition must have module locked in
Base Timing Mode).
4. What is the idle mixture screw setting?
5. Is the engine idle speed rpm correct?
6. Is venturi cluster discharging fuel by 2000 rpm?
7. Is a good stream of fuel being discharged by both discharge holes
in venturi cluster when throttle lever is moved repeatedly while the
engine is off.
8. Does the engine flood at idle?

Flooding At Idle RPM

If your engine floods at idle rpm, check the following:
1. Problem in ignition system causing engine to run rough.
2. Idle mixture screw adjusted incorrectly.
3. Bad needle and seat.
4. Incorrect float level or drop.
Needle / Seat Change
MerCarbs are factory equipped with a spring loaded needle. If the preceding steps did not
correct your problem, change to the solid type needle.
Needle and Seat Assemblies
Index
90-861327--1 OCTOBER 1999
a - Spring Loaded Type Needle (Kit 3302-9029)
b - Solid Type Needle (Kit 3302-9407)
MERCARB 2 BARREL CARBURETOR
Y
Y
Y
Y
Y
Y
Y
a
b
N
N
N
Turn.
N
N
N
N
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