Orfice on fryer tube has flame on it

The things you will want to check and correct are the burner venturi, this is where the gas and air mix (where you see the flame when it backfires), this being dirty or clogged will cause this problem, your burner at the top being dirty can also cause this. Also, be sure the orifice is clean. If possible you should also check the gas pressure and set it accordingly. The other thing to check is the burner tubes themselves, these are the tubes that go through the fryer, many times with this scenario the tubes are getting clogged. These tubes being clogged will not necessarily cause this problem, but you may as well clean them while you are there.