when i switch mine off i some times hear a little flame type noise in the exhaust, when setting mine on the dyno we had to remove all the plugs and clean them they were black and as sooty could be, the car got to the point it would not start after that headway was made with good results
Can,t recommend a dyno enough best £160 i spent would not have got them right without it.
Going back soon when my new ignition is fitted to make sure i get every last bhp extracted
Dan