Final answer:
The H and L screws on a carburetor control the air-fuel mixture at different engine speeds. The H screw adjusts the mixture at higher speeds, while the L screw adjusts it at lower speeds.
Step-by-step explanation:
The H and L screws on a carburetor are used to adjust the air-fuel mixture. These screws control the amount of fuel that is mixed with the air entering the engine.
The H screw, also known as the high-speed screw, controls the air-fuel mixture at higher engine speeds, such as when the throttle is wide open. By turning the H screw clockwise, you can decrease the amount of fuel, making the mixture leaner, while turning it counterclockwise increases the fuel, making the mixture richer.
The L screw, also known as the low-speed screw, controls the air-fuel mixture at lower engine speeds, such as when idling. Similar to the H screw, turning the L screw clockwise makes the mixture leaner, while turning it counterclockwise makes it richer.