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The anti-back-fire solenoid is sometimes confused with a fuel shutdown solenoid. A fuel shutdown
solenoid on a diesel engine stops the fuel supply to the engine and is the main component to shut the
engine down.
On a gasoline engine, the engine is shutdown by grounding the ignition coils secondary winding. During
engine run down, as the piston travels downward in the cylinder; vacuum is still being created in the
carburetor. This vacuum continues to drawn raw fuel into the engine and to the hot muffler. Since the
fuel does not combust in a controlled burn without the spark ignition, the fuel can then ignite from hot
spots in the muffler. This explosion; or uncontrolled burn during engine run down is called "back-fire".
The fuel will continue to be drawn through the engine until the engine comes to a complete stop.
The anti-back-fire solenoids job is to prevent the fuel from being drawn into the cylinder during engine
run down. Anti-back-fire solenoids can function in two ways; as a "power to run" or a "power on
shutdown". The Honda engine solenoids used on Multiquip GA series generators operate on a "power
to shutdown".
The anti-back-fire solenoid works by electromagnetism and a spring. During normal engine operation
the spring holds the pintle inward. With the pintle held in; the fuel can pass into and through the
carburetor. During engine shutdown, the solenoid becomes energized. With direct current passing
through the coil of the solenoid, a magnetic field is created. This magnetic force in the coil overcomes
the spring force holding the pintle inward. The pintle now is pushed outward by the magnetism, blocking
the fuel jet orifice in the carburetor. The blockage of this orifice prevents fuel from being drawn into the
engine during rundown.
Anti-Back-Fire Solenoid
Summary of Circuit Function
The power source for this circuit comes from the engine accessory lamp coil. When the flywheel,
containing magnets, rotates past this lamp coil, an alternating current is induced into the coil. The
alternating current flows to a full diode rectifier located in the control panel. This converts the alternating
current into a useable direct current. Direct current is needed to form a magnetic field in the anti-back-
fire, or fuel cut solenoid. Once converted to a direct current, power flows to the main operation switch.
When the switch is closed, the circuit to the anti-back-fire solenoid is complete; as is the ignition coil
circuit completes direct to ground. With the operation switch in the off position and the circuit now
closed, power flows through the anti-back-fire solenoid coil creating a magnetic field. The magnetic field
influences the pintle in the solenoid causing it to extend into the carburetors fuel orifice.
Testing the Anti-Back-Fire Solenoid
Testing the solenoid can be done by applying DC voltage. The use of a 12V battery or 9V battery can be
used. Place the positive lead from the battery to the solenoid lead and a negative lead from the battery
to the solenoid case, or in two wire type solenoids, connect to the negative lead.
A properly functioning solenoid will have a sharp distinct movement and normally have an audible
"clicking" sound when the power is applied.
Multiquip Inc. ◦ GA Series Generators ◦ Manual No. GAGENSM
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