Solenoid Troubleshooting Guide
Manual 36541
6
Woodward
Shutdown vs. Throttle (Choke) Applications
Shutdown applications control via the fuel shutoff lever. The lever controls fuel flow
to the engine or application. Usually a relay in the engine start system switches from
the pull coil to the hold coil. However, over cranking by the operator can burn out the
solenoid and therefore including a timing device is preferred as a safety measure.
Throttle (Choke) applications use a solenoid to increase the amount of fuel going to
the engine. It pushes or pulls the throttle control lever to a preset position. With an
externally switched solenoid, a timing device (such as a Coil Commander) to switch
from the pull coil to the hold coil is needed to limit the pull coil on time. As an
alternative, an internally switched solenoid can also be used.
Shutdown solenoids are prone to failure because of over cranking by the operator,
resulting in overheating, while throttle solenoids are prone to failure because of likely
problems in the system.
Coil Protection
In an internally switched dual coil solenoid, the pull coil is energized at the same
time as the hold coil, with the key switch in the “Run” position. The plunger switches
off the pull coil when it bottoms out, provided there is enough voltage and the
linkage is adjusted correctly.
In an externally switched dual coil solenoid, the hold coil is designed to be energized
continuously with the key switch in the “Run” position. There is little or no danger of
the hold coil failing.
The pull coil is designed to be energized for a short time during engine cranking with
the key switch in the “Start” position. Thus, the pull coil current is considerably
higher (30-50 amps depending on the model) than that of the hold coil.
Energizing the pull coil causes a significant rise in the internal temperature of the
solenoid. Burnout of the coil can occur with excessive engine cranking. Therefore,
the pull coil must be turned off, as soon as possible, after pulling the plunger to the
“bottomed out” position.
For both internally switched and externally switched solenoids, it is recommended
that engine cranking be limited to three 30-second attempts with a cool-down period
of two minutes (120 seconds) between each cranking attempt. After three cranking
attempts (total elapsed time of 5½ minutes), the solenoid must be allowed to cool
down to ambient temperature before making further cranking attempts.
