Time for an update - already.
I have been over the timimg and ignition with a fine tooth comb / checked and re checked, gap and timing are spot on, all connections good, tried 2 different coils, 3 different plugs, 2 plug caps and 2 leads. I also returned the ignition to the factory arrangement i.e. took out the "points assist" module. Also made sure that the battery was well charged.
Under
all permuations of plugs / coils / caps etc the result was the same, it would run for about 10 seconds, and then die due to a very wet plug.
This has convinced me that it is either carburation releated (despite new jets & fuel level being correct), or possible that the cases have a crack that I did not see that is allowing oil to be drawn in from the gearbox. I have tried it without the filter and I get exactly the same results - an oiled plug, so not the filter.
Someone is going to lend me a good known to be OK carburettor which I am going to try, but before I do that I am going to walk away from it for another week or so.
If it still has the same problem with the known to be Ok carb fitted then it has to be drawing oil in from the gearbox, and if that is the case, I will probably put it up on E-Bay as a non runner, at this point however I remain optimistic.........but think I have had that optimism once before