Try (my website!) here: http://www.retrospecparts.com/101-fixings
I've got M7 nuts and a few other bits and pieces.

Citroen do like to use strange sizes like M7 & M9, and these are hard to get hold of other than from a 2cv specialist.
The nut on that bit of carb is more likely to be M4 or M5 though, and they're very common, you'll probably find a box of them in the local bricolage.

Joolz,
you've got to blame Solex (carb folk) for that one, not Citroen.

M8 x 1, plus it's a half nut to add insult to injury...

ken

That was most definitely the problem ( I know it should have been more obvious) and now after several days of testing it starts first time every time.

I have done a basic tune up of the carb but is there anywhere on here that shows a step by step on get the mixture correct as well as the timing.

Also, how do you figure out rpm when it says in the instructions "adjust to 650 rpm etc etc" Is it just a fell, i.e very slow chugging

Thanks for the help - another snag sorted.