On all vehicles equipped with adjustable ignition timing and an adjustable idle speed the two processes of adjusting the idle speed and the ignition timing are very closely related and affect each other closely. When performing either of these adjustments, it is usually necessary to adjust each in a back and forth manner since they affect each other. For example, if the ignition timing is adjusted the idle speed could increase past what is recommended. This in turn could affect actual ignition timing during normal use of the vehicle, which would affect the vehicle's driveability. Therefore, the idle speed would have to be adjusted, which could in turn affect the ignition timing. Eventually, after adjusting each back and forth a few times to reach the desired specifications, they will meet both specifications simultaneously. Most often they only need to be adjusted a few times before both are correct.
NOTE: The throttle valve adjusting screw should not be tampered with unless the carburetor has been rebuilt. This screw is preset and determines the relationship between the throttle valve and the free lever, and has been accurately set at the factory. If this setting is disturbed, other service adjustments cannot be done accurately. Also the improper setting (throttle valve opening) will increase the exhaust gas temperature during deceleration, which in turn will reduce the life of the catalyst greatly and deteriorate the exhaust gas cleaning performance. It will also effect fuel consumption and engine braking.
WARNING
Since the cooling fasn is disconnected, be extremely cautious about the length of time the engine is allowed to idle. Check the temperature gauge often and turn the ignition OFF if the engine starts to overheat.