Weak magnets possibly? There was probably nothing wrong with the original set up. Most of the time you just have to burnish or replace your points and reset them to .020 and ocasionally the replacment of the condencer.
Be sure you have the coil to flywheel spacing is correct. I think .010 is the spec. but I use a business card. Lossen the coil and pull as far away from the flywheel as possible and tighten the screws. Turn the flywheel so the magenets are below the coil, slip business card between the coil and the flywheel and loosen the screws. After the coil has been atracted to the flywheel tighten the screws. Now turn the flywheel to remove the business card and check your spark.
I change the condencer out for a new one before I went to the electronic one.I am gaping it to close I allways just got it as close as possible .010 to .015 should do OK.I think the big problem is there was rust on the flywheel.I have cleaned it off with sand paper and wire brush and it could be the magnet.I have a flywheel off of a vertical one.Does any one know if this could be a permanent fix or temporary.