I have an MTD Yard Machines snow thrower that wont turn over or start. It seems to not be getting any spark. I have installed 3 different brand new ignition coils and still no spark. I'm assuming the new coils were bad. Is it common to get that many bad parts? Is there a way to test the coil before I take it from the store? FYI- the engine is a Tecumseh HSSK50 67376P (H). I have also wire brushed the rust off of the flywheel, and the area where the coil mounting screws attach. I disconnected the wire on the coil that attaches to the grounding circuit-still no spark.