The engine is cranking over just fine, we have great spark, it’s getting fuel and air just fine. The engine sometimes fires and then will quit for some time. Very random firing, when it fires it will not stay running. It seems to have no effort to try to start and just sounds like it’s cranking. Although we did find 3 dead mice in the exhaust and the air box was completely full of house insulation. We need some help to figure out why it is not firing m.