A safety system for engine powered machinery having a fuel cut functionality to promote more rapid shutdown of the rotating parts of the engine powered machinery. In one aspect, the system is implemented as a wiring harness disposed exclusively on the engine which simultaneously disables one or more ignition coils and prevents a fuel-air mixer from supplying a mixture of air and fuel to the engine upon activation of a safety switch. In alternate aspects, the system further comprises a stator brake which is activated by the safety switch to provide additional braking torque on the engine. These features bring the machinery to a rapid halt, further enhancing safety.

A carburettor for supplying an internal combustion engine, comprising a diffuser in a form of a venturi tube (90), which is provided with an inlet port (91) for air and an outlet port (92) of an air/fuel mixture, characterised in that the inlet port (91) of the diffuser (90) is partially closed by a diaphragm (10) having a passage hole (11) exhibiting a smaller diameter than a diameter of the inlet port (91).

A fuel metering system for a combustion engine carburetor utilizes a non-convoluted, planar, flexible diaphragm which does not require a molding process to form a traditional convolution. The diaphragm defines in part a pressure controlled fuel metering chamber on one side and a reference chamber at atmospheric pressure on the other side. During operation of the engine, sub-atmospheric pressure within a fuel and air mixing passage draws fuel from the metering chamber to mix with air for combustion within the engine. As pressure within the metering chamber thus decreases, the diaphragm flexes into metering chamber. The displacement of the diaphragm actuates a flow control valve of the metering system which flows pressurized make-up fuel into the metering chamber until the diaphragm returns to its datum position. Preferably, hardware of the flow control valve which is in direct contact with a surface of the diaphragm exposed to the metering chamber does not penetrate the diaphragm as the traditional rivet and washer assembly would. Therefore, manufacturing costs are reduced and any opportunity of leakage between the fuel metering chamber and reference chamber is eliminated. Preferably, the carburetor is of a manual external purge type in order to exert sufficient vacuum within the metering chamber to displace the metering diaphragm thus opening the flow control valve to purge the carburetor of unwanted fuel vapor and air prior to starting the engine. The novel planar diaphragm thereby resolves problems associated with traditional metering diaphragms such as variation in convolution datum height affecting flow control valve lever/diaphragm clearances, non-symmetric convolution axis or distorted convolution affecting diaphragm pressure response and recovery.