Anytime the point gap changes, the timing changes with it. For every one degree of "dwell" change (the amount of distributor rotation the points are closed) the timing at the crankshaft changes two degrees. If your point dwell (gap) is changing rapidly, something else is wrong. There could be a worn bushing in the distributor, or simply a "soft" rubbing block on the points or a rough distributor cam that's wearing the rubbing block away rapidly.
As with any other diagnostic process, eliminate possible problems one at a time instead of rushing off in all directions. Good luck!
Jerry
