The safe thing is to disconnect the line and plug the carb port. Most systems do not have vacuum draw at idle. Be sure to set the idle speed before setting timing. If idle speed changes after setting timing, reset idle speed and adjust timing again. These two interact some. When done, unplug carb and reconnect the vacuum line. While you have the line disconnected and the timing light is operating, rev engine and determine that the mechanical advance is working correctly. It should be smooth and not jump around. Also do this after the vacuum line is connected to check the combined effect of mechanical and vacuum advance.
Posted on Sep 7, 2011, 11:55 AM from IP address 126.96.36.199