Amal Concentric Carburettor (T140V)

[kembo]

Call me stupid but work this one out. I know I will in the end but.........
The throttle valve (slide) is sticking i.e. full throttle and then it wont drop back down.
Get this if I put the valve in upside down it doesnt stick at all.

I have started to file what I think are high spots.

Any suggestions as to  why it goes in easy one way and sticks the correct way?