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A Yamaha YFZ450 ATV relies on a single spark plug to operate its engine. Under normal circumstances, the spark plug is fairly durable and can provide hundreds of hours of reliable service. However, Yamaha recommends a monthly inspection of the spark plug to avoid possible engine failures brought about by a damaged or failing spark plug. If the spark plug is damaged in any way, it must be replaced immediately. Only a few tools are necessary to remove and replace the spark plug, but you may need to make a few adjustments to the plug before it can be installed.
Step 1
Unlatch the seat, using the release lever at the rear of the seat. Lift the rear of the seat up, and then pull it away from the ATV.
Step 2
Unscrew both upper fuel tank cover bolts, located below the handlebars, using a 5 mm Allen wrench. Unscrew the lower fuel tank cover mounting bolts, using a socket wrench and a 10 mm socket. Lift the fuel tank cover slightly, and then pull it toward the rear of the ATV until it can be removed completely.
Step 3
Unscrew the mounting bolts from the left and right side covers, located below the fuel tank and the ATVs seat rails, using a socket wrench and a 10 mm socket. Pull the side covers away to access the fuel tank mounting bolts and the engine.
Step 4
Unscrew the upper fuel tank mounting bolts, located in front of the handlebars on the ATVs frame, using a 5 mm Allen wrench. Lift the front fuel tank cover away from the fuel tank. Unscrew the lower fuel tank mounting bolts from the ATVs seat rails, using a socket wrench and a 10 mm socket. Set the tanks fuel valve to the "Off" position, and then pull the fuel hose from the valve outlet. Lift the fuel tank off the ATV.
Step 5
Reach between the ATVs seat rails and grasp the ignition coil, positioned on the top of the engines cylinder. Pull the ignition coil off the spark plug. Unscrew the spark plug, using a socket wrench and a 16 mm spark plug socket.
Step 6
Check the new CR8E spark plugs gap, using a gap tool. Your YFZ450 requires a gap range of 0.028- to 0.031-inch. If the spark plug gap is not within this range, bend the spark plugs electrode slightly with the gap tool and recheck the gap.
Step 7
Screw the spark plug into the engine by hand. Tighten the spark plug to 9.4 foot-pounds, using a torque wrench and a 16 mm socket wrench. Push the ignition coil over the top of the spark plug.
Step 8
Mount the fuel tank onto the ATV. Screw the lower fuel tank mounting bolts into place with a socket wrench and a 10 mm socket. Tighten the lower mounting bolts to 5.1 foot-pounds, using a torque wrench. Place the front tank cover over the fuel tank, and then screw the upper mounting bolts into place with a 5 mm Allen wrench. Push the fuel hose onto the fuel valve outlet.
Step 9
Install the left and right side covers onto the ATVs frame. Screw the side cover mounting bolts into place with a socket wrench and a 10 mm socket. Tighten all of the side cover mounting bolts to 5.1 foot-pounds, using a torque wrench
Step 10
Slide the fuel tank cover over the fuel tank and around the handlebars. Screw the upper mounting bolts into place with a 5 mm Allen wrench. Screw the lower mounting bolts into the ATVs frame, using a socket wrench and a 10 mm socket.
Slip the seats mounting tongue under the base of the fuel tank, and then lower the seat onto the seat rails. Press down on the rear of the seat until the seat latch locks.
Warning
- An improperly gapped spark plug can affect the ignition timing and cause misfires. Always check the gap before installing the spark plug onto your YZF450s engine.
Items you will need
- 5 mm Allen wrench
- 10 mm socket
- Socket wrench
- 16 mm spark plug socket
- CR8E spark plug
- Gap tool
- Torque wrench
