Use the KISS method first...
Keep
It
Simple
Stupid
Look to the the big three first. Spark, air, fuel. If an engine has these three things, in the right combination, it should run. If it has all three, but one is out of synch, then it won't run...If the A/F ratio is wrong, it should still fire over, but may either run like crap, or only run for a second or two. Your issue is not this as it runs fine for a decent amount of time. So, this pretty much eliminates the fuel portion of the equasion(sp). (Of course, like dirt said, it COULD be clogging up as it goes along...But it is unlikely...Same deal with the fuel pump. both are possible, but not likely) so, with the air "ok", and the fuel "ok"...That leaves the sparkerator.
Now, issues can and often DO happen with the electrical system. This is the most likely weak link in the system. Then, we look to the most likely PARK of this "most likely weak link" in the system. The plug wires, and then the dizzy and the parts ON the dizzy. Now I have seen a car, with the TFI going bad, have spark, but the car still didn't run. Because the TFI was causing it to throw spark at the wrong times because it was going bad.
This little part gets my vote...and at the cost, I would say it's a winner. I'm waiting on pins and needles to find out.
