Quick update..... only had time for a quick look this afternoon, I fired her up and she ran ok for a min or two, then dropped onto one cyl again..... so I started by taking the plugs out (quite awkward to get at the rear one.... ) the running cyl plug looked ok, the non-runner was black and oily... anyway i cleaned them both and switched them..... ran it again for a few mins and seemed ok.... Some of my 2 stroke buddies who run RGV's TZR's etc seemed to think that the problem could well be sparkplug related, i was a bit dubious that it would be so simple but maybe i'm going to be lucky.... I'll order some new plugs in any case....