i have heard some poor things on here about some of the stuff from brands hatch performance but haveno experience of them myself so cannot comment, the screw should only beplayed with whilst using an analyser otherwise its as accurate as sticking your finger out of the window to gauge wind speed lol. my old cossie was doing similar thou i gapped the plugs to 0.6 that stopped any back firing , but it turned out to be my map sensor at faut causing the overfuelling, it was that bad the oil was being topped up with petrol!!