ignition problems - what to try next?

I have run out of ideas as to what is keeping my Mustang from starting, so hopefully someone can point me in the right direction. Here's some background on my problem.

Over the last few months, I have noticed that my car would struggle to start from time to time, and sometimes it would have fluctuations in rpm at idle. I suspected the points needed to be replaced, so last month I replaced them and made a 400 mile trip over the same weekend with no problems at all.

After that weekend I didn't drive the car for a month, and last week when I tried to fire it up it would crank but would not start. Since the logical source of the problem would be the points, I replaced them with a new set and gapped them properly, but the engine would still not fire. I tried turning the distributor small amounts in both directions to see if that would make a difference with no luck. Yesterday I got a multimeter to test the ignition coil as a friend cranked it, and the car fired right up! The timing was off obviously (the engine would start to miss around 2500 rpm) but it would run, and the engine started without problem on subsequent attempts. I tested the coil, and it was showing fluctuating voltage between 4 and 9 volts at idle. Since I don't have a timing light at home, my plan was to drive the car to base and take it to the shop today to set the timing.

Well, when I tried to start the car this morning it was the same old story; cranking, but no start. There are so many things that could cause this problem and I am not sure what to try next. The engine is getting fuel and it has a spark. I need help from someone who has some experience with this sort of issue. Please let me know if you have any ideas!

When I first purchased the car from my uncle 9 years ago, it had an MFD ignition. The problem with the electronic ignition was that since the engine still used a generator the electronic ignition was actually more troublesome than the points ignition. I rebuilt the engine 4 years ago and kept the generator and points and up until last week I never had a problem with that setup. As crazy as it sounds, the points are going to stay and I know that there is some other problem lurking that is causing the starting issues.

mustangman, thanks for suggesting to check the regulator. I could not get the engine started to check on tuesday, but I did check the spark plugs. They had a little carbon on them and inline with normal wear, but I decided it was a good time to replace the plugs and wires anyway. After that the engine started up, I was able to drive around the block, and I was able to drive it to work today to get the timing set.

I reset the initial timing to 12° BTDC and the engine idles fine now at 650 RPM. I checked the regulator and it was showing a good output, but the coil still has a fluctuating 3-9 volts across the terminals. Also, the engine will start to stumble around 4000 RPM. Could this be caused by a coil not providing a constant voltage to the distributor? Or could this be a result of too much mechanical advance? If so, what do I need to do to get the mechanical advance back to normal? In any case, I think the old coil needs to go.