Page 150 - REPOWER REFERENCE GUIDE (2020)

Fuel System
Boat Fuel System Inspection

Inspect the components of the boat's fuel system as indicated below. Clean, repair, or replace items as required.
Fuel Tank
• Condition and cleanliness
• Construction material
• Pickup tube and screen
• Vent line
• Antisiphon valve (refer to MerCruiser Service Bulletin 99‑7)
Fuel

• Age and condition of the fuel in the tank
• Ethanol percent content in the fuel (refer to Section 1B ‑ Use of Reformulated Fuel: Alcohol In Fuel
Recommendations)
NOTE: Use Mercury alcohol fuel tester 879172T28 to verify the percent of ethanol in fuel.
Fuel Line

• Condition of the line—must meet SAE 1527
• Safely secured, with shortest length possible
• Minimum fuel line diameter:
• Single engine: 10 mm (3/8 in.) inlet
• Dual engine: 13 mm (1/2 in.) inlet
Fuel Delivery System
The fuel delivery system must be designed to deliver the fuel to the engine with minimal restriction and at the lowest
temperature. Gasoline is extremely sensitive to vaporizing if placed under a vacuum (low pressure) and exposed to moderate
or high temperatures. This is particularly true if winter blend fuels with a high RVP (Reid Vapor Pressure) are encountered in
warmer temperature areas. Excessive restriction in the fuel delivery system may cause a condition known as vapor locking.
This typically occurs after the engine has been operated at high RPM and then shut off and allowed to sit for 15 minutes to 2
hours. During this time the engine heat soaks, causing the temperature of the fuel system to increase. Upon restart, the
combination of heat and vacuum in the fuel system causes the fuel to vaporize. The fuel system cannot handle this vapor and
therefore, fuel starvation results when the boater attempts to resume operation. Depending upon the degree of vapor locking,
this can range from a hesitation or bog when accelerating to a complete stalling of the engine. To minimize the potential for this
problem, the guidelines should be observed to limit fuel delivery restriction to 6.9 kPa (1 psi) or less and fuel inlet temperature
to 44 °C (110 °F) or less.
The fuel delivery system is an integral part of the boat. Mercury MerCruiser makes no attempt in this manual to cover all
aspects of design and integration of the fuel delivery system, due to broad range of possible configurations and the numerous
regulations and standards that cover this area. The applicable standards and regulations for the markets where your product
will be sold should be observed, along with any information from the fuel system component manufacturers. The following
general guidelines are provided:
! WARNING

Improper boat design and construction may result in serious injury or death. Adhere to all applicable marine regulations
(United States Coast Guard [USCG], European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards they
reference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers [SAE], International Standards
Organization [ISO], etc.) when designing and constructing the boat and other components, such as the engine compartment,
fuel delivery system, or exhaust system.

Safety is the main concern in the design of a boat's fuel system. This must be achieved through a technically sound installation
and constant inspection.
The fuel system, from the filler pipe to the fuel pump, is the same, in principle, for all boats.
The fuel tank is an integrated component of the boat. Refer to the special information on service and maintenance that you
have received from the tank manufacturer.
Only a few points related to function and safety are listed here (refer to boating standards [NMMA, ABYC, etc.] and Coast
Guard regulations for complete guidelines):
• All connections should be on the upper‑side of the tank.
• The drain plug at the lowest point on the tank permits the removal of water and sediment.

Page 6B-2 © 2019 Mercury Marine 90-8M0149179 eng NOVEMBER 2018