Harley-Davidson EVO may be backfiring on the rear cylinder because it has a wasted spark system. If fuel and electrical is all good/correct it is often the case in these symptoms that motor cycle spark plugs that although looking good and firing outside of the engine are breaking down and will not fire under compression pressures on a power stroke but will fire unburned fuel on the unpressurized exhaust stroke when the plug again fires in a wasted spark ignition system and when so firing the result is a backfire, usually quite loud.
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Harley-Davidson EVO may be backfiring on the rear cylinder because it has a wasted spark system. If fuel and electrical is all good/correct it is often the case in these symptoms that motor cycle spark plugs that although looking good and firing outside of the engine are breaking down and will not fire under compression pressures on a power stroke but will fire unburned fuel on the unpressurized exhaust stroke when the plug again fires in a wasted spark ignition system and when so firing the result is a backfire, usually quite loud.