The carburetor on a two-cycle motor, like the motor on a Craftsman chainsaw, regulates the quantity of fuel that enters the combustion chamber. This is an important function, because the wrong combination of air and gasoline creates incomplete combustion and poor engine operation. The adjustment process isn’t complex, but you want to get a tachometer, or even a relatively straightforward job can become a frustrating and potentially damaging one.
Carburetor Adjustment Screws
The carburetor on a Craftsman saw is comparable to the one on most two-cycle engines since it has three adjustment screws. Among those screws, which is arranged at the apex of a triangle, adjusts the idle speed whereas another two regulate the total amount of fuel that the carburetor sprays once you depress the throttle trigger. The low-speed screw sets the fuel ratio for low-speed performance while the high speed screw sets the ratio for maximum motor speed. The high-speed adjustment is critical for operation; if it isn’t right, the saw may stall when cutting orcutting at the other extreme, burn itself out by running too quickly.
Adjusting the Screws
When adjusting the carburetor, you usually set the idle screw. When the setting is right, the motor continues running once you release the throttle without causing the string to spin. The low-speed adjustment, which you also make while the motor is idling, refines the slack adjustment. If it is too rich, the motor overloads with dies and fuel, and if it is lean, the motor races, and in the extreme, stalls and dies. You have to engage the throttle and run the motor at full power to make the high-speed adjustment which, similarly, overloads the motor with fuel when it is too affluent and causes the motor to race when it is lean.
The Need for a Tachometer
While a seasoned lumberjack might get an ear for optimum motor operation, most other individuals, including service staff, use a tachometer to ranking motor rank. This apparatus either clamps on the spark plug wire or detects the fire of this plug remotely and steps engine speed by documenting the fire cycle. It gives you an accurate measurement of motor speed to complement the intuitive awareness of engine operation you profit by listening to this motor rank. Accuracy is particularly important when setting the high-speed screw, since a misadjustment can quickly burn out the engine.
Tips and Reminders
The only other tool you want to adjust a Craftsman chainsaw carburetor is a flat-head screwdriver. It’s very important to dimension the screwdriver properly; if the tip is too thick, it wo not fit in the screws and you might wind up stripping the heads. Be aware that the maker sets the high-speed setting at the factory and does not recommend changing it. In fact, but the carburetor falls out of adjustment after several hours of service and needs tweaking to keep optimum saw performance. Moreover, if it has been set for sea level, the saw wo not operate correctly at altitude if you don’t adjust it.