Craftsman offers a line of lawn and garden equipment, including lawn tractors, walk-behind lawn mowers and snow blowers. Craftsman lawn tractors use a comparatively large engine, often started by an electric starter. The carburetor on a Craftsman lawn tractor mixes the gasoline with air before the mixture is drawn into the cylinder through the intake valve. If the engine is running roughly, you may need to adjust the carburetor to help the engine run more efficiently and smoothly under any workload.
Turn off the engine if it is running, and lift up on the engine cowling from the end near the steering wheel to tilt it open.
Loosen the screw on the top of the air filter canister with a flat-head screwdriver, and lift off the canister from the top of the carburetor.
Locate the idle adjustment screw on the side of the carburetor. Gently rotate the screw clockwise until it stops turning, using a flat-head screwdriver. Do not over-tighten the screw, as it could damage the seat. Back the screw off in a counter-clockwise motion one-and-one-half turns.
Turn the main adjustment screw underneath the carburetor's float bowl. If your carburetor has one, it will be a large round bowl on the bottom of the carburetor. Turn clockwise until it stops turning. Back the screw off counter-clockwise one-and-one-half turns.
Locate the high-speed adjustment screw. If your carburetor has one, it will be on the opposite side of the carburetor from the idle adjustment screw. Turn the screw clockwise until it just touches the seat, then back it off counter-clockwise one-and-one-half turns.
Replace the air filter on the top of the carburetor, but leave the engine cowling open.
Start the engine, and let it warm up at idle for about five minutes. When the engine is warm, gradually turn the idle adjustment screw clockwise until the engine begins to slow. Back the screw off counter-clockwise past the point where the engine runs normally until it begins to slow once again. Turn the screw clockwise to a point halfway between the two points where the engine began to slow.
Increase the throttle to full speed, and perform the same adjustment with the high-speed adjustment screw.
Close the engine cowling, and test the tractor under varying workloads. The engine should run smoothly under high speed or at idle.