The Kawasaki FC420V engine, a tiny 14HP motor, is a lawnmower power plant. If you have lawnmowers with this type of engine, you have probably encountered problems with it. Fortunately, you can solve most problems with small gasoline powered engine with a few simple and inexpensive solutions. For a motor to run, three components must work in synergy: fuel, air and electricity. Put these elements should first when troubleshooting engines.
Check whether you have enough fuel in the gas tank. Trace the fuel lines by removing the ends attached to the carburettor. Let the fuel out for a few seconds, and watch for any obvious clogging--an essential component especially when you have stored your mower for long periods, as gum deposits from old gasoline tend to build up in the fuel line up to the carburettor.
Remove the air filter, and check whether fuel is reaching the carburettor inlet. If you don't sense any traces of fresh fuel inside, check whether fuel is coming out of the main jet by actuating the throttle lever. If still nothing comes out, remove and disassemble the carburettor completely, check whether the needle is stuck and spray all fuel lines with a carburettor cleaner. Reassemble and reinstall it.
Locate the air mixture screw. This is usually found at the back of the carburettor. Fully turn the screw to a close by turning clockwise, then turn the screw counter-clockwise to about 1½ turns.
The FC420V engine has a stock Mikuni carburettor. You will see two screws on either side of the carburettor. The flathead screw is the air mixture screw. Turning it clockwise makes the air-fuel mixture rich, while turning it counter-clockwise makes it lean.
Remove the two screws on top of the carburettor air filter, and take out the filter element. Replace the air filter if it looks dirty and already worn. Never run the engine without a fuel filter.
Remove the spark plugs using a sparkplug puller and visually inspect the plug tip for any oil or fuel. Check for excessive carbon build-up. Clean the spark plugs by soaking it in gasoline, then clean the electrode and gap with a wire brush or a fine sanding paper. To check if the spark plug is still good, connect the plugs to the high tension wire and place it about quarter-inch near any exposed metal surface of the engine. Crank the engine and check for sparks jumping from the spark plug tip to the open metal surface. If you see sparks, your spark plug is good. Screw it back to the engine.
When checking for spark, be sure the tip of the spark plug is about 1/4th of an inch or closer to any unpainted metal part of the engine. Placing it farther than 1/4th of an inch might cause the sparks to miss reaching the other end which could cause minor electrical shock.