Backfiring is a startling explosive sound that can happen when you shut down your lawn mower or other small-engine-powered equipment. Fuel shutoff solenoids prevent engines, including the Kohler brand, from backfiring. By effectively blocking fuel flow to the carburetor when the ignition key switches to the "Off" position, excess fuel can't enter the combustion chamber, eliminating the potential for that annoying noise. If backfire still occurs, the fuel shutoff solenoid is suspect and requires investigation.
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Lower the throttle to the mid-range position just before shutting the Kohler engine down. In order for the fuel shutoff valve to work properly, the throttle position should be in the full to mid-range position. If a backfire occurs despite following the proper shutdown procedures, check for proper voltage.
Test for a minimum of 7 Volts DC at the fuel solenoid terminal using a Volt-Ohm meter. Place one of the meter leads to the solenoids terminal, and the second lead to the engine case. Power from the battery shuts the fuel flow off to the carburetor. No power is present on the solenoid while the engine is running. If no (or low) voltage is present at the solenoid, check the battery for proper charge and for good battery connection.
Test the battery for voltage using the Volt-Ohm meter. Attach the Volt-Ohm meter across the positive and negative battery posts while the engine is shut down. Crank the engine and observe the voltage drop across the battery posts. If the voltage drops below 9 Volts DC, apply a battery charger and bring the battery back to its appropriate charge. Replace the battery if it will not accept a charge.
Remove the fuel shutoff solenoid from the carburetor for further testing if the above tests reveal no problems. Connect 12 Volts DC power to the solenoid. Connect the negative (ground) lead to the solenoid case, and apply the positive (red) lead to the solenoid terminal. If the solenoid does not shift to the "Off" position, the solenoid is bad and replacement is necessary.
Check the fuel supply and fuel filter if engine fails to start before troubleshooting the fuel shutoff solenoid.
Use extreme caution when working around fuel and a battery source--even a small spark will ignite the fuel.