UPDATE.
Stripped the valve gear, re lapped the vavle slider, reset the timing marginally, fired up the steam, the engine wouldn't self start, and it wouldn't run on less than 20psi, (model boiler gauge). There is still a tight spot on the engine, and all my gaskets on the steam chests now leak steam slightly, not much, but still too much, disturbed too many times I think, the seat to the cylinders and valve chest is good, (lapped).
Adjusted the valve sliders slightly with the engine running and got the engine running a bit smoother, but not perfect. All in all the running was lumpy, certainly not smooth enough for me., any way it wouldn't self start, so whats the point in having two cylinders if you still have to spin the fly wheel. I'm a bit peeved because I took my time sorting the bottom end, but there is still something causing a tight spot. I saw one of these engines running on air before I bought mine, and that was tighter, but it ran smoothly, so I'm still thinking its timing that is the the main problem.
I think the next stage is to strip the top from the bottom, and re check the crank, for tight spots AGAIN. And take it from there, rebuild from the bottom up.