Bleeding The Fuel System - Lehman SP90 Owner's Manual

FIG. 4.
TYPICAL FUEL SYSTEM, TURBO ENGINES
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A Injection pump return tube
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B Filter Press Relief Line
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C Injector Leak Off Line
*NOTE: "ON ENGINES MADE IN LATE 1985 ONWARDS
TO SIMPLIFY PIPING" (Return line to tank must be 10mm bore min.)

Bleeding the Fuel System

Bleeding air from the fuel system may well be one of the important procedures to be learned by the operator. Air
in the injection system may cause erratic engine performance, "missing" on one or more cylinders, reduced power,
stop fuel from reaching engine and prevent or cause hard engine starting.
It must be remembered that the lift pump draws fuel from the tank, so any accumation of air in the fuel system
makes all connections, filters, etc. between fuel lift pump and tank suspect. In any new installation one must "bleed"
the system of air for, obviously, air will be in the new fuel lines, filters, etc. If the fuel tank should run dry, bleeding
will be needed when the boat is refueled. Bleeding will also be required after changing fuel filter elements. (Time
and effort may be saved if filter is charged with fuel by removing the bleed plugs on top and slowly pouring fuel
into the filter until it overflows.) Occasionally, after an extended run, an engine may slow down, or "miss", or lose
RPM or stop. Although there may be other causes, air in the fuel system should not be overlooked. Many times a
tiny leak in a fuel line fitting may allow air to enter the system and accumulate until there is sufficient to cause the
above mentioned symptoms.
To bleed system, follow this procedure;
1. Ascertain that there is sufficient fuel in tank, (Note: low fuel level may result in intake pipe being exposed due
to "sloshing" of fuel, thus drawing air into system
2. Make certain that fuel shut-off valve is turned on.
3. Loosen the bleed screw on the inlet side of the fuel filter (Fig. 6 & 7 ) about two or
4. Operate the priming lever at the side of the fuel lift pump on naturally aspirated unit (Fig. 7.) or the pump plunger
(Fig. 6.) on turbocharger engines until a flow of fuel, free of air, is expelled. Then close screw.
No bleeding of the injection pump is required as these are fitted with a self purge device.
NOTE: On Turbo Charged engines a third fuel return line from the pressure relief valve or the secondary filters
must be connected direct to the fuel tank. This is obligatory unless a factory fitted common return is present.
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FUEL RETURN LINES MAY BE INTERCONNECTED
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try to keep your tanks topped