Dave,
Well it would appear it's either no spark or no fuel. When it fizzles out for the last time and you can't get it to go, you will have to see what 'isn't there...fuel or spark! When this happens, put your meter between coil - and a ground, then crank away! If you want to take the other route, when it happens, squirt a little fuel into the carburetor and see if it springs to life.
I can see no connection between your generator troubleshooting and this problem. I think it must be written off as coincidental. Your rig has a 12 volt battery and the negative is connected to ground... you have no doubts that the generator, regulator and other items were also swapped to 12 volt.
Coils and condensers can be sensitive to heat and fail when warm. It didn't sound like the engine ran long enough for things to get hot...if you have a 12 volt coil, it wouldn't take much to stick it on and erase any doubt you might have. The test I mentioned above with the meter on the primary lead wire would tell you if the coil was sound. Keep at it!
Stuart
