tyhjäkäyntisuuttimen

Tyhjäkäyntisuutin, known in English as an idle jet or pilot jet, is a critical component within the carburetor of an internal combustion engine. Its primary function is to deliver fuel to the engine when it is operating at idle speed or at very low throttle openings.

During idling, the engine draws relatively little air through the carburetor's main venturi. The main fuel circuit, responsible for providing fuel at higher engine speeds, is largely inactive because the airflow is insufficient to create the necessary vacuum. The tyhjäkäyntisuutin, however, is specifically designed to operate under these low-vacuum conditions. It is a small, precisely machined nozzle that allows a small, controlled amount of fuel to mix with the incoming air.

This fuel-air mixture is then fed into the engine through a separate passage, often called the idle circuit or pilot circuit, which bypasses the main venturi. The amount of fuel delivered by the tyhjäkäyntisuutin is determined by its orifice size. A larger orifice allows more fuel, leading to a richer idle mixture, while a smaller orifice restricts fuel flow for a leaner idle mixture.

The proper functioning of the tyhjäkäyntisuutin is crucial for smooth engine operation at idle. If it is clogged or worn, the engine may idle poorly, stall, or exhibit rough running. Conversely, an incorrectly sized tyhjäkäyntisuutin can lead to an overly rich or lean idle condition, affecting fuel economy and emissions. It is a common maintenance item, and cleaning or replacing it is often part of carburetor tuning and repair.