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SECTION - 4
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 (2 in. Hg) 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 a
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:
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.
The main concern of a boat's fuel system is safety; 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, which 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 serves to permit the removal of water and
sediment.
•
The tank breather pipe must have an inner diameter of at least 13 mm (1/2 in.) and must be
fitted with a swan neck to prevent water from entering the tank.
It is recommended that the exact route and length of the fuel lines be established at the first
installation of the engine to prevent problems later in connecting them to the engine.
All fuel lines must be well secured. The holes where the lines run through the bulkheads should
be carefully rounded off or protected with rubber grommets. This prevents damage to the lines
from abrasion.
The following, but not limited to the following, additional fuel connection related points, applying
to all engines unless otherwise stated, must be considered [Refer to boating standards (NMMA,
ABYC, etc.) and Coast Guard regulations for complete guidelines]:
1. Fuel pickup should be at least 25 mm (1 in.) from the bottom of fuel tank to prevent picking up
impurities.
90-899883183 DECEMBER 2007
WARNING
!
FUEL SYSTEM
Page 3 / 6
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