[Anthony]

Make sure the weights/springs are mobile on the mechanical advance, so you know you're getting full mech advance.

You need to know what your total advance should be, ? 32-34 degrees, but whatever it is, you need to set your engine timing at that. With the vacuum advance hose disconnected, hook up your timing light, and gradually rev your motor, watching the timing advance until it stops advancing, and that is your rpm when full advance is in, and adjust your distributor(twisting it), at that rpm, to your target timing setting. Your distributor is now timed correctly.

The vacuum advance is only for cruising, that is, it only kicks in at partial throttle to even further advance the timing, even more, to get better mileage, as under partial throttle, your engine can tolerate more advanced timing for better power,economy. However, under full throttle, the engine vacuum drops, and therefore the vacuum advance drops to zero, as under full throttle, the engine cannot tolerate the "more" advanced setting the vacuum advance will provide, which could result in damage to the engine.