A drill should do it. I have done so in past and had no problems. So you now can look elsewhere. The ignition on these small motor's is quite simple. Coil, magnet, spark plug or ignition lead (wire). This is just a total shot in the dark......... could you have a broken spark plug wire inside the jacket and the cold or reposistioning of the wire is giving intermitant contact? When you got this spark, was it when you were outside, or on the bench?. Sometimes the cold will contract metal pulling a break in the lead apart.

If you have spark and you have fuel, the only other thing I can think of would be, is there a chance that your flywheel has no key and when installing it on your plane you reposistioned the flywheel and changed the timing?

Just a couple of guesses. Peter