The cut-off valve ensures that the engine does not continue to run when the ignition is switched off. This can only happen when the engine is hot.
To check if the valve is still working, turn the ignition on or connect it to 12 volts (the housing part is the ground), if you hear a click, it is still working, if you don't hear anything at all, the valve is broken. In the case of the by-pass air cut-off valve, you can also see it on the piston that moves during operation.
If your carburetor has an idle jet and the engine is not running or is running rough, also holding back between 70 and 80 km/h, it is likely that the jet is clogged and needs to be cleaned.
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