I realise this thread is a little old, but with the carby picture you have there I think the float is installed upside down. From memory the brass fork part that is visible in the photo should be straddling the groove in the needle.
You probably already know that and this picture was just there for another purpose but I thought just in case I better mention something
No worries Dave, you're right, that was just for the photo, I did have it the right way when I tried to test it.
