No it's the 'Air Jet' as referred to on the site (somewhere!!!). It's the large brass tube below the main jet/emulsion tube when looking at the carb from the bottom. It does not have a slot in the end for removal with a screwdriver. It's size number (on mine anyway) is *55.

I have managed to carefully clean it out by using a carb jet cleaning tool set. It now allows me to suck air through it, similar to the other carb. I then used brake cleaner spray to try to clean away any debris.
This would have been a more confidence inspiring move with this Air Jet removed.

Mike
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I don't mind dying...I just don't want to be there when it happens!