I have no idea with gas systems but it ran perfectly on gas until it backfired and died, now will not run at all. Also will not run on fuel. All plugs spark, coil pack is fine. Fuel pump and filter are fine. Checked all leads, vacuum hoses and everything and they are all connected. Engine will start and run on fuel but only if I take a spark plug out so obviously it runs horrible. Engine sounds like it wants to start as soon as I turn the key but then will die instantly both on fuel and gas. Please help.