With a dial back timing light you can set the knob to zero and then read the timing mark flashes on the scale by the crankshaft. Say for instance the timing mark is lining up on the 8 deg mark on the scale. Now keep squeezing the trigger and turn the timing knob on the light. As you turn it, the timing mark on the balancer ought to appear to start moving toward the zero on the scale on the crankshaft scale. If everything is reading correctly, when you get the timing timing mark on the balancer lined up with the 0 on ths scale, the knob on the timing light should be pointing to 8 deg in this example.
The advantage of the dial-back light is that you do not need the balancer to be marked with a complete scale of numbers. Most cars only have a small timing scale that may go from 20 deg BTDC to 4 deg ATDC or something similar. If you are checking timing at higher rpm's, the timing will be off the scale on the crankshaft indicator. With the dial back light, you can dial the timing light knob until the timing mark on the crank is lined up with the timing scale by the crank and you can read the timing on your timing light instead of of having a balancer that having a series of timing marks.
If your car has the Load-a-matic, you need to replace it with a 1968 or later distributor. Your carb is not compatible with the Load-a-matic and if the timing is advancing all the time, it sounds like you may have the load-a-matic. On a non-load-o distributor, you can run it without the vacuum line to the distributor as long as it is plugged. But your mileage and performance will suffer. I have a car that does not have vacuum advance, but the engine is set up more for racing applications than street.
Doug
