a) Connect the tachometer to the engine;
b) Start the engine;
c) Make sure the engine runs smoothly;
d) Clamp the vacuum hose of the vacuum switch;
d) Gradually increase the engine speed and check that the engine starts to run rough;
e) Release the pinched vacuum hose and increase engine speed again; make sure the engine runs smoothly;
g) With the engine idling, disconnect the solenoid valve electrical connector and check if the engine stalls/runs rough;
h) Stop the engine and connect the electric wire to the fuel shut-off solenoid valve. Disconnect the tachometer.
2. Check the vacuum switch.
a) Using an ohmmeter, check for continuity between the switch terminal and its housing.
The original can be found on this resource [TOYOTAMAN]
b) Start the engine.
c) Using an ohmmeter, check for continuity between the switch terminal and its housing. If there is any, replace the switch.
3. Check the fuel shut-off solenoid valve in the primary chamber of the carburetor.