Aware of the vital importance of cleaning out the trap regularly, I repositioned it on top of the inlet manifold for easy access.
However, what I failed to realise is that it also acts as a mini-trap for oil, and oily vapour that has been drawn up through the oil separator tends to condense and accumulate there. I was puzzled by the brief puff of blue smoke on pulling away after decelerating to a stop in second, especially downhill. I did the inlet valve seals, but found they made no difference. Then I had this hunch about the flame trap. I had repositioned it above the manifold, but horizontally, in line with the pipe connecting to the air intake.
I realised this was a mistake. What seemed to be happening was that oil built up in the trap on deceleration, then on opening the throttle it was sucked into the air intake.
I think it is very important that the flame trap is mounted vertically, in line with the oil separator, so that any oil can run straight back down again.
I moved the trap again, also incorporating another wider reservoir (actually a spare bulb from a carburettor Pulse Air system) and the oil "injection" has stopped.