Fuel System Desription
1965 Evinrude 90HP StarFlite outboard
Fuel Flow
The Starflite 90S fuel system consists of fuel tank, fuel pump, and carburetor.
The fuel tank is non-pressurized, suction operated. A diaphragm-displacement type fuel pump on the motor draws fuel from the tank and furnishes it to the carburetor through a fuel filter.
Carburetor
The carburetor is a four-barrel, side-draft type with straight-in manifolds to each cylinder. High-speed jets are fixed. Separate low-speed jets for each barrel are linked together for simultaneous adjustment.
A separate float bowl and needle valve control fuel to each barrel.
Leaf Valves
There are four individual leaf block assemblies, one for each cylinder, but all attached to a common leaf plate base. Each leaf block assemblies has twin 4-segment leaf valves attached, one on each side. The entire assembly is mounted between the crankcase and intake manifold. The entire assembly may be removed for inspection and repairs.
Automatic Choke
The carburetor is fitted with an automatic hot air choke to reduce the ratio of air to fuel for cold starts. Four choke valves, one in the air inlet of each barrel, are mounted to a common choke shaft. An adjustable bi-metal spring is located in the choke housing, and the setting of this spring is controlled by the choke knob on the top of the carburetor. With the choke knob in the "OFF" position, the choke valves are held in a fixed open pOSition, allowing air to pass freely through the inlet. With the choke knob in the "ON" position, the valves are held in a closed position, restricting the flow of air to the carburetor. However, suction in the crank- case will operate against the spring tension, allowing some air to pass through. With the choke knob in the "AUTOMATIC" position, the choke will be held closed when the motor is cold. As the motor warms up, heat from the exhaust chamber is passed through the heat exchanger tube to the choke housing, causing the spring to allow the choke to open.
A choke solenoid, mounted at the bottom of the carburetor, closes the choke valves when the choke switch is depressed. The choke solenoid operates the choke valves through a spring, allowing the choke to open partially as crankcase suction increases.
Fuel Pump
The fuel pump is of the diaphragm-displacement type, and is operated by changes in crankcase pressure. Alternate suction and pressure in the crank-case are transmitted to the pump diaphragm through a flexible hose. Suction created on the upward stroke of the piston causes the diaphragm to displace and draw in fuel through the inlet valve. On the following downward stroke of the piston, crankcase pressure flexes the diaphragm in the opposite direction. The inlet valve is then seated, preventing the return of fuel to the tank, while the discharge valve is opened, allowing fuel to pass to the carburetor.
Fuel is drawn through a fine mesh filter before entering the pump to remove impurities.
Updated on: Saturday, November 21, 2020