The Yamaha WR 450-F is a 449-cc liquid cooled four-stroke motocross dirt bike. On the lower right side of its carburetor is an adjustable air screw, which controls the gas-air mixture. The bike owner’s manual features a chart that will detail how many turns to the right or left you need to turn it according to your altitude and type of riding.
Tools Used: Tools, Owners manual, Flat head screwdriver
Adjust the Fuel Screw
Determine the number of turns needed for the air screw based on your altitude. This is available in the related chart, located toward the end of the bike’s owner’s manual.
Turn the gas valve on the left side of the engine to the “on” position. Start the engine and allow the engine to warm for about two minutes. Turn the screw to the right until it is snug using the screwdriver. Then, turn the screw to the left the number of times dictated by the chart.