Sticky choke

[uber]

Hello all

I've noticed that the choke on my B4 has started to stick open when the chokes closed, so was wondering if anyone had any tips or advice on "unsticking" it? The bike was having some work done on it last week so I asked the mechanic to have a look but its still sticking!

I know I can get a replacement for about £14 so I can change it if I have to - is it difficult? Otherwise has anyone got any advice?

[PitterB4]

Is the cable binding up in the sleve or the linkage on the carbs?  This is probably pretty obvious but I'd start by lubing both.