Each post so far has been about more problems - but not this one!! Today I checked all nuts etc were tight, and took the cyliner tops off to check the basic timing. When I did this I found that the internal part that slides over each steam hole (they probably have a proper technical name unknown to me) seemed to be slightly scuffed. It was the base plate (in which the holes are drilled) which was scuffed, which I assumed was down to insufficient lubrication from the lubricator. I thoroughly oiled the whole cylinder block, sealed it back up and hey presto it ran much better. I also worked far harder to drive the loco - before I had tried to find a single regulator setting that would give power for the curves but not too much power for the straights. This time I added power before the corners and almost closed the regulator for long straights. Its like a different loco now!! And when I undid the nuts steam came out!! I guess its more lubrication, tighter steam line nuts and better driving!!! Thank you to everyone for their help.