Turn on the ignition.
Plug (253) remove one by one from a separate shut-off valve (21) several times and put it on again. In this case, the valve should click audibly.
Otherwise, connect a test lamp between the plug and ground. If the lamp lights up, replace the valve. If the lamp does not light up, then check fuse No. 14 or electrical wiring according to the wiring diagram.
Start the engine and let it idle. Remove the plugs on both valves at the same time, the engine should immediately stop without running any further. Start the engine again and remove the left valve plug, the engine speed should drop significantly or the engine will start to twitch. Then put the plug on the left valve and remove it from the right one, the speed should also drop. Otherwise, replace the corresponding valve.
Caution: On carburetors without a central CO adjusting screw between the idle cut-off valves, the valves can be replaced with the carburetor installed.