- 1). Look for a spring-loaded screw sticking out of the carburetor side. Use a screwdriver to remove the lid of a carburetor box if your carburetor is enclosed. Start the scooter engine and let it idle a bit until warmed up.
- 2). Use a flat-head screwdriver and insert it into the spring-loaded screw. Turn the screw a quarter-turn to the left. Listen for the engine turnover to increase in speed. Turn it two quarter-turns to the right. Listen for the engine turnover to decrease. Turn it completely over to the right to cut off air and kill the engine.
- 3). Decide the appropriate position of the spring-loaded screw to obtain a clean-running idle on the engine. If your scooter has a tachometer, turn the screw until the engine hits close to 1,500 rotations per minute (rpm) on the dial. Speed up the engine if it continues to sputter or die out. Close up the carburetor box when done.
- 1). Turn on the scooter and let it idle. Look for a small, exposed screw on the opposite side of the carburetor from the idle speed screw (on old carburetors like Dellorto assemblies, the air-fuel mix screw will stick out of the top in an obvious way).
- 2). Use a flat-head screwdriver to make adjustments. Turn the screw one-eighth of a turn per adjustment and listen to the engine idle speed. Turn it to the right to cut off air and turn it to the left to add air to the mix.
- 3). Listen for the idle speed to change accordingly and cut the air if the idle speed begins to pick up too much speed. Adjust the jet to allow more air if using the scooter in a high altitude area. Adjust it downward if you intend to use the scooter in a low sea-level area after changing from a high altitude.
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