I assume this is an older 3W-100 with one magnet on the crank hub. This means the old style ignition. This ignition uses an inductive pickup coil for a sensor and requires some rpm before it will spark. If you remove the plugs to test for spark, you have to give the prop a healthy flip. Also, test in a dark location. The spark is a little feeble and it's impossible to see in sunlight. The system grounds through the outer cap metallic shield, so you don't have to hold the plugs against the engine when testing - just make sure you put the plugs in the plug cap.