The ECU/Engines mission is to achieve stoichiometric combustion at all RPM and load ranges, We all know thats not 100% possible, i don't think it should quite be spitting flames though. However, its normal to throw fuel down the pipe when on the limiter, as it cuts the spark not the fuel. But, realistically, it doesn't take much of an over fuel to cause a backfire, and were not talking about "new" lean burn engines here..... so i think to see flames, is kind of "normal" considering the straight through pipe