MST Marine Fuel Systems Flashcards

What is the correct procedure to test a fuel system for leaks after a repair?

Answer: Pressurize with air to no more than 3 psi and check fittings with soapy water

A low-pressure air test (max 3 psi) with soapy water applied to fittings safely reveals leaks without the fire risk of using fuel.

Phase separation in ethanol-blended gasoline (E10) stored in a marine tank causes what problem?

Answer: Water and ethanol separate from the gasoline and sink, leaning out the fuel mixture

When water is present, ethanol absorbs it and separates from the gasoline layer, creating a water-ethanol mix that can damage engines and fuel systems.

A two-stroke outboard engine is drawing in air through the fuel system; which component is the most likely cause?

Answer: Cracked or deteriorated fuel line or primer bulb

Air infiltration in a two-stroke fuel system is almost always caused by cracked fuel lines, a deteriorated primer bulb check valve, or a loose fitting.

What is the function of the anti-siphon valve installed on a marine fuel system?

Answer: To prevent fuel from gravity-feeding into the engine when it is not running

The anti-siphon valve closes when the engine stops to prevent raw fuel from flooding the engine or bilge via gravity flow from the tank.

What color is the standard fuel fill deck fitting on gasoline-powered boats to distinguish it from diesel?

Answer: Red

ABYC standards specify red deck fill fittings for gasoline to prevent misfueling with diesel, which would damage gasoline engines.

When replacing a fuel filter on an EFI outboard engine, what precaution must be taken before disconnecting fuel lines?

Answer: Relieve fuel system pressure by running the engine until it stalls or using the service manual procedure

EFI systems maintain residual pressure in the fuel rail; pressure must be relieved before disconnecting lines to prevent fuel spray and fire risk.