My concern that it was not leak tested was in your best interest.
I possibly has no relation to the spark problem, but if you fix the spark, start it and ride with an air leak, you will have a bigger problem!
Maybe you could have broken the HT wire where it goes into the plug boot.
Take the boot off by unscrewing it and cut off about 1/2" of the wire, then screw to boot back on.
There is a possibility that the Woodruff key has been sheared from multiple backfires, you may find that you need to lap the flywheel.