MerCruiser 350 CID (5.7L) - User Manual

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Number 24

Printed in U.S.A. 90-861327--1 1099

1999, Mercury Marine

GM V-8

305 CID (5.0L) / 350 CID (5.7L)

MARINE ENGINES

SERVICE

MANUAL

MAIN MENU

Table of Contents

Questions and Answers

J
juarezyolandaAug 4, 2025
Why is the acceleration of my MerCruiser 350 CID (5.7L) poor?
- S
  storresAug 4, 2025
  If your MerCruiser Engine's acceleration is poor, several factors could be the culprit. Begin by adjusting the idle mixture screws and checking/correcting the ignition timing. Inspect the intake manifold or carburetor base for any vacuum leaks. Replace any fouled, burned, or cracked spark plugs, ensuring they match the correct heat range. Also, check for a stream of raw fuel from the accelerator pump discharge nozzle when opening the throttle with the engine shut off. Replace a dirty or cracked distributor cap or rotor, and clean the carburetor if it's dirty. Low compression may also be a factor.
J
john47Aug 8, 2025
What to do if my MerCruiser 350 CID (5.7L) fluctuates rapidly at idle?
- L
  Lindsey AdamsAug 8, 2025
  If your MerCruiser Engine fluctuates rapidly at idle but steadies as RPM increases, the valve guides may be worn. Inspect and replace worn valve guides to resolve this issue.
J
Jennifer MillerAug 13, 2025
What to do if my MerCruiser 350 CID (5.7L) Engine fluctuates slowly at idle?
- A
  Adam BerryAug 13, 2025
  If your MerCruiser Engine fluctuates 4 or 5 inches very slowly at idle RPM, it could be due to several reasons: The carburetor may need adjustment, the spark plug gap might be too narrow, or the valves could be sticking. Try adjusting the carburetor, checking the spark plug gap, and inspecting the valves.
T
Timothy KiddAug 17, 2025
What to do if MerCruiser 350 CID (5.7L) has extremely low reading at idle?
- J
  josephgreenAug 17, 2025
  If your MerCruiser Engine shows an extremely low but steady reading at idle RPM, possible causes include a vacuum leak, incorrect timing, an underpowered boat, or a faulty boat bottom. Inspect for vacuum leaks, check the timing, and assess the boat's condition to address this issue.
M
Matthew LopezAug 21, 2025
What to do if my MerCruiser 350 CID (5.7L) fluctuates between high and low at idle?
- K
  karen35Aug 21, 2025
  If your MerCruiser Engine reading fluctuates between high and low at idle RPM, it indicates a blown head gasket between two adjacent cylinders. Inspect and replace the blown head gasket to fix this issue.
T
Tina PittsAug 26, 2025
What to do if my MerCruiser 350 CID (5.7L) fluctuates at regular intervals at idle?
- M
  Michael CooleyAug 26, 2025
  If your MerCruiser Engine continuously fluctuates between low and normal readings at regular intervals at idle RPM, this could be due to a burned or leaking valve. Inspect and replace the burned or leaking valve to resolve this issue.
B
Brenda OrtizAug 30, 2025
What does a steady reading mean for my MerCruiser Engine at idle?
- L
  Lisa TurnerAug 30, 2025
  A steady reading between 15-21 inches at idle RPM on your MerCruiser Engine is considered normal.

Summary

IMPORTANT INFORMATION

Section 1 B - Maintenance

Details maintenance schedules, intervals, tools, lubricants, fluid capacities, fuel recommendations, and storage procedures.

Section 1 C - Troubleshooting

Lists common engine problems, their causes, and diagnostic procedures for troubleshooting various symptoms.

REMOVAL AND INSTALLATION

ENGINE

Section 3 A - 350 cid; 5.0 L; 305 cid; 5.7 L Engines

Provides detailed specifications, torque values, and disassembly/reassembly procedures for the engine and its components.

ELECTRICAL SYSTEMS

FUEL SYSTEM

Section 5 E - Fuel Injection Disassembly And Reassembly

Provides detailed procedures for disassembling and reassembling fuel injection system components.

Section 5 F - Fuel Injection System Troubleshooting

Offers diagnostic procedures and troubleshooting charts for common fuel injection system problems.

Section 5 G - Diagnostics

Outlines diagnostic tests, trouble codes, and circuit checks for various engine systems.

COOLING SYSTEM

EXHAUST SYSTEM

DRIVES

Section 8 A - Velvet Drive In-Line And V-Drive Transmission

Provides specifications, identification, torque, fluid requirements, and procedures for removal and installation of Velvet Drive transmissions.

Section 8 B - Velvet Drive 5000 Series Transmission

Details specifications, identification, ratios, fluid requirements, torque, and procedures for servicing Velvet Drive 5000 series transmissions.

Section 8 D - Drive Shaft; Propeller Shaft Models

POWER STEERING SYSTEM

MerCruiser 350 CID (5.7L) Specifications

General

Engine Type	V8
Displacement	350 CID (5.7L)
Ignition System	Electronic Ignition
Horsepower	250-300 hp (depending on model and year)
Fuel System	Carbureted or Fuel Injected (depending on model and year)
Bore x Stroke	4.00 x 3.48 inches
Compression Ratio	9.4:1

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