Bill, while I dont own a 3, the situation should be generic. If you have a
vacuum gauge, disconnect the fitting at the advance unit and hook up the gauge
to verify you have vacuum getting to the valve. You should probably see
between 10 - 15 lbs of vacuum at idle. If you dont have a gauge, you will
probably feel some suction if you put your finger over the open end of vacuum
line. If you are getting vacuum, reconnect the vacuum line and hook up a
timing light and point it at the timing marks. You should see the timing mark
move toward retard as you incease the throttle, then toward advance when you
let off the throttle. Or if you have a vacuum pump, you can use it to pull a
vacuum on it and see if it holds vacuum. If you use the pump while the engine
is idling, you should see a change in engine speed as you pull a vacuum on the
advance unit. If not, the advance unit is kaput.
John Lumia - 1976 TR6
What's the best/easiest way to verify operation of the vacuum advance on a
TR3A distributor? Can the diaphrams be replaced or repaired?