For all the posters who keep suggesting more nitro - I have read repeatedly that in Europe / UK the price of nitro makes it a rare commodity, and the engines are tuned to run with no nitro at all.

TerrellFlyer is right - 1.5 turns is merely a reference point to help get you started. It sounds like it is running a bit lean. Open the needle valve 1/8th of a turn and see if it runs better. Also, ABC engines need to run slightly hotter than ringed engines, to get proper compression. My favorite engine (also ABC) will not run reliably under 10°C. That isn't a problem for me though, since I don't like freezing my fingers.