Carburetor: Almost all chain saw carburetors have three adjustment screws: a low-speed mixture needle (labeled L), a high-speed mixture needle (labeled H), and an idle-speed screw (I or T) that is larger than the others and pushes against the carburetor linkage, rather than terminating within the carb body. Generally, you should have to deal with only the idle-speed screw. If the engine idles either too slowly and stalls, or so fast that it drives the chain. (The engine should idle evenly with the chain stationary.) If you have to adjust the mixture screws, slowly turn them in (clockwise) so that they seat very lightly, then back them off (counterclockwise) one turn. Now, if the engine stalls under acceleration, the low-speed needle should be opened slightly. If it races at idle (with the idle-speed screw properly set), the high-speed needle needs to be opened. Racing indicates a too-lean mixture that can damage the engine. Smoking signifies richness, and the needle(s) should be turned down slightly. If you're not quite sure what to listen or look for, have the mixture settings adjusted by someone familiar with the saw.
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