There is a part of the linkage that looks like a rod with a spring on it. This is supposed to rest on a pivoting "hook", but is often left loose and allowed to drop down. This is referred to as the "teeter totter". If you conduct a search, you should find info on it. This is you most likely suspect.
You can also do some more research over at
www.sterlingmetalworks.com , where there is a wealth of information on Nikki carbs.
Good luck.
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