Checking the spark by hooking the plug wire to the plug and grounding the plug against the block will only prove that your spark will jump the gap on the plug. You should use the coil wire against the block to get a better feel for how much voltage is coming from the coil. The spark should jump at least a 1/4 inch gap, and be a thin blue/white spark. If is a fat yellow spark and wont jump much of a gap that imay not be enough to start the engine. Keep in mind, that compressed air acts like an insulator, and a spark that will jump the plug gap when the plug is outside the engine may not fare so well when it is under compression.
Are you sure the engine is getting enough fuel at startup? The sputtering at first then stady cranking with no response sounds like you need more fuel into the engine.
Are you sure the engine is getting enough fuel at startup? The sputtering at first then stady cranking with no response sounds like you need more fuel into the engine.