2 stroke engine will only run on choke?

I have a Jonsered GR50 brushcutter/strimmer which will only run on choke. As soon as I give it revs the choke automatically disengages & the engine stops straight away. I have taken the muffler off & it was well choked up with coke but after cleaning it's still doing it. tried another carb & still the same.

Any help much appreciated.