Thanks for advice Jaffa. The choke extends around 1 -1 1/2 inch. moving it a small way has no effect. only when fully extended does it have an effect.
I have tried numerous combinations of trying to start - but it always seems reluctant. I have had other bikes and used choke alone which has worked fine, but not with this bike. Something is wrong.
a) Trying to start bike with no choke - Bike will start but not tick over until its been started a few times. If you try and increase throttle too quickly it stalls. After very slowly increasing the throtlle the revs climb, and then the idle becomes stable. All ok.
b) Trying to start bike with full choke - the bike starts then stalls immediatley. ( as if flooded)
c) tyring to start bike with half choke - bike will eventually start but tick over does not become stable until throttle is increased and the bike revved.
The best method ive found so far is to coax the throttle so the revs increase, then fully extend the choke so that the bike ticks over fast. One running for a short time i close the choke and all is ok.
Once warm the bike idles at around 1500 rpm. - I have tried adjusting the tick over but this doesn't seem to help starting.
Once bike is warm it runs lovely, just something wrong with start up.