[FC] vacuum advance question

[Wild8bill at aol.com]

After setting the timing using a timing light, I noticed that when I rev  the 
engine that the timing retards very far very fast (from 14 btdc to -4 btdc),  
and kind of "catches up" to where it should be over a few seconds. The  
vacuum advance appears to move instantaneously, however. If you give it too much  
gas too fast, it dies. Is this a symptom of a bad vacuum advance, or bad 
vacuum?  Yes, I did check for vac leaks.
 
Note: thanks to everyone for the ideas about the electric fuel pump, new  
pump is on and fixed the problem.
 
Bill
'61 rampside
'63 greenbrier