Thanks for all the answers.
I had a feeling it was because the bearing I'm using is flat where as the original is curved.
It is central with the clutch plate as I made the mounting on my trusted Myford and doubled checked, my double check which was doubled checked by the lad before putting it all together.
Well it's engine back out again for the (insert big number here) time and a trip to the local motor factors where I hope I can find an assistant willing to look through his stock for a suitable bearing, unless anyone on here knows what bearing would work.
In the meantime I'll see if I can graft the original bearing onto the concentric cylinder and give that a try.
On a brighter note the electronic fuel injection seems to be working, which has the added advantage of being able to limit the revs while the engine is run in.