has spark and fuel, wont start.

I just converted from points to the later model electronic ignition box/distributor, and had it running bitchen. shut it off and turned it on several times. I come out a couple hours later to go out to my clubs cruise night and the car wont start. I checked for spark and its there. There is fuel in the filter, and even tried Carb spray down the carb. Very rarely I will get a cough like it wants to start. But nothing. I cracked the old brittle ballast resistor while pulling the terminal off, but it worked when I first fired it up. I'm not sure whats wrong, there is fuel and spark but no fire