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MerCruiser 305 CID (5.0L) - User Manual

MerCruiser 305 CID (5.0L)
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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

  • C
    Christopher PerezJul 25, 2025
    Why is the acceleration of my MerCruiser 305 CID (5.0L) Engine poor?
    • S
      Susan HutchinsonJul 25, 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.
  • D
    david75Jul 29, 2025
    What to do if my MerCruiser Engine fluctuates rapidly at idle?
    • P
      Peter GeorgeJul 29, 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.
  • K
    Kevin DavisAug 3, 2025
    What to do if my MerCruiser 305 CID (5.0L) fluctuates slowly at idle?
    • W
      williamsmichaelAug 3, 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.
  • D
    Derrick HinesAug 7, 2025
    What to do if MerCruiser 305 CID (5.0L) Engine has extremely low reading at idle?
    • J
      James TorresAug 7, 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.
  • L
    Lori VillanuevaAug 11, 2025
    What to do if my MerCruiser 305 CID (5.0L) Engine fluctuates between high and low at idle?
    • A
      Amanda LesterAug 12, 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.
  • M
    Mark McgeeAug 15, 2025
    What to do if my MerCruiser 305 CID (5.0L) Engine fluctuates at regular intervals at idle?
    • E
      Elizabeth FisherAug 16, 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.
  • J
    Justin CowanAug 20, 2025
    What does a steady reading mean for my MerCruiser Engine at idle?
    • S
      Stephen RobertsonAug 20, 2025
      A steady reading between 15-21 inches at idle RPM on your MerCruiser Engine is considered normal.

Summary

Section 1 C - Troubleshooting

Engine Cranks Over but Will Not Start or Starts Hard

Provides a troubleshooting guide for engines that crank but do not start or start with difficulty.

Charging System Inoperative

Troubleshooting steps for a non-functional charging system, including battery, alternator, and regulator checks.

Engine Overheats (Mechanical)

Outlines mechanical causes of engine overheating, such as incorrect timing or lubrication issues.

REMOVAL AND INSTALLATION

ENGINE

ELECTRICAL SYSTEMS

Section 4 A - Starting System

Information on the starting system, including components, maintenance, testing, and troubleshooting.

Section 4 B - Ignition System

Details on the ignition system, including components, specifications, and troubleshooting.

Section 4 C - Charging System

Information on the charging system, including precautions, identification, specifications, and testing.

FUEL SYSTEM

Section 5 A - Fuel Delivery System For Carbureted Engines

Details on the fuel delivery system for carbureted engines, including identification, specifications, and components.

Section 5 B - Mercarb 2 Barrel Carburetor

Information on the Mercarb 2-barrel carburetor, including identification, specifications, and service procedures.

Section 5 C - Fuel Delivery System For Electronic Fuel Injection

Details on the fuel delivery system for electronic fuel injection engines, including components and procedures.

Section 5 E - Fuel Injection Disassembly And Reassembly

Procedures for disassembling and reassembling fuel injection system components.

Section 5 F - Fuel Injection System Troubleshooting

Troubleshooting guide for fuel injection system symptoms and diagnostic procedures.

Section 5 G - Diagnostics

EXHAUST SYSTEM

DRIVES

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

Section 8 B - Velvet Drive 5000 Series Transmission

POWER STEERING SYSTEM

Section 9 A - Pump And Related Components

MerCruiser 305 CID (5.0L) Specifications

General IconGeneral
BrandMerCruiser
Model305 CID (5.0L)
CategoryEngine
LanguageEnglish

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