Greg, the firing voltage required does increase with higher air pressure around the plug. That is why you are supposed to test the ignition system with a plug gap of 0.060", compared with the 0.025-0.030" you use on the actual spark plug. So trying a known good plug is a worthwhile step in a situation like this. Note that a new plug is not necessarily a good plug - we've had a few defective new plugs reported here recently.
Leshby, have you tried the priming test? Have you checked the flywheel key? Those items were on my initial list of tests to make, half a dozen posts ago, and you haven't reported on the results.
