The carburetors of small single-cylinder engines are factory set for average operating conditions. They can, however, be out of order. (Non-contractual photo, does not necessarily reflect the drawing)
The original setting may not be appropriate for a specific use, for example in the mountains, or in very hot weather.
In this case, the carburetor must be adjusted. This operation is also required after any disassembly of the carburettor. When first starting, after wintering, it is also recommended to check the setting.
Start the engine and let it run at its normal working speed for about 5 minutes, then stop the engine. If it is a four-stroke engine with a regulator, loosen the stop screw on its link and push it to the maximum open position of the throttle; With the linkage held in this position, turn the control axle all the way and tighten the set screw. Start the engine and set the maximum speed by acting on the adjusting screw.
This scheme is indicated in the Maintenance Manual mower; it is generally in the range of 3,000 to 3,200 rpm for four-stroke gasoline single-cylinder engines. You can measure it using a tachometer connected to the ignition circuit. After setting the maximum speed, adjust the idle speed, using the carburetor idle screw. For a two-stroke engine, also heat the engine, then stop. With a screwdriver, turn the high speed mixing screw all the way to the right until it stops, but do not force it. Do the same with the low speed screw, then turn it to the left about 7/8 turn.
Put the engine back on, slowly bring the throttle to the bottom, then release the command: the engine must run smoothly at idle.
Carburization sometimes goes off by itself. In addition, engine and spark plug wear and variations in fuel quality may require adjustments to the carburetor settings. Some clues are indicative of a maladjustment.
The engine refuses to accelerate: on a four-stroke engine, adjust the wealth screw; on a two-stroke, act on the low-speed screw by turning it to the left. If the engine suffocates as soon as you accelerate, also check the idle speed adjustment. If these adjustments prove ineffective, it is necessary to disassemble the carburettor to check the main jet, probably clogged. On a two-stroke engine, the origin of the phenomenon can be found at the accelerator pump diaphragm: if it is altered, it must be changed.
The engine lacks power: he refuses to reach his maximum speed when working under normal conditions. This comes from a fuel mixture too poor in fuel.
On a two-stroke engine, adjust the high-speed adjusting screw, turning it to the left, and slowly stop as soon as the smoke in the exhaust gets thicker.
On a four-stroke engine, first check the regulator setting. This symptom can also betray a partial obstruction of the arrival of gasoline. Check the Hose and fuel filter. Beforehand, check the gap between the electrodes of the spark plug, which remains the main source of engine power drop.
The engine smokes excessively: in principle, this phenomenon can only occur with a two-stroke engine. On a four-stroke, it corresponds to excessive wear of the segmentation, which also results in difficulty starting, lack of power and significant oil consumption.
On a two-stroke, excessive smoke, with a motor fed by a correctly dosed mixture, is corrected by acting on the high-speed mixing screw, which must be turned to the right; stop as soon as the engine speed starts to fall.
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