The carburettor diaphragm plays a key role in the engine fuel supply system because it provides precise pressure regulation and even metering of the fuel and air mixture. Over time, due to exposure to aggressive components and additives in petrol, the diaphragm material loses elasticity, becomes brittle, stretches or cracks. When the diaphragm wears out, the engine starts to draw in false air, which leads to hard starting of a cold engine, rough idling (so-called "surging" and fluctuating revolutions) or complete loss of power under load. Fitting a quality Oregon replacement diaphragm restores factory performance and stability of operating modes, offering a significantly longer service life than cheap, unbranded copies. When replacing the diaphragm, it is necessary to completely clean the carburettor of deposits of dirt, petrol gum and water. Pay special attention to the order of assembly: the gasket and the diaphragm itself must lie exactly in their positions without twisting or shearing where the screws pass through. Tighten the carburettor cover screws in a cross pattern and gradually so that the pressure on the diaphragm is completely even across the entire seating surface, which prevents fuel leakage and air ingress. Key characteristics Part type: Carburettor diaphragm Manufacturer: Oregon (high-compatibility, high-quality aftermarket part) Catalogue number (OEM): 270026 Replacement code: US-99302 Diaphragm length: 55 mm Hole diameter: 4 mm Compatible models Garden machinery and mowers with Briggs & Stratton engines: Briggs & Stratton 5 HP (engines of 5 horsepower with the tank under the carburettor)