Yipee!! stripped the carb and found the jet just to the front of the main jet (pilot jet?) was completely blocked. poked it through with a bristle from a wire brush and the jobs a good-un !
Thanks for all your help. Now I just need to learn to ride the bugger.

Manual??
I thought english language manuals were unobtainable!

Thanks for the replys. I'll check the bed for muddy footprints!!
I forgot to mention that it will rev with the choke on and run fairly normaly.
Does this rule out stale petrol?

I havent started my crm for about 6 months. Decided its time to get out on it again, but bugger! It starts OK on choke but dies when I turn the choke off. HELP!!!