Is that not just the mixture screw? I will admit I'm a d*** s***, but I can follow instructions from a book, and to my way of thinking a screw ain't a jet, but again you could be correct LOL cheers Dennis 
You are correct. The screw meters the amount of air fuel mixture on idle.
Your best friend here is a vacuum gauge plug it in the brake vacuum hose. Mess with the screw until you get the highest vacuum on the gauge.
This is after the engine spark timing is correct.
Ok if you don’t have a vacuum gauge. Another very old school way of setting the idle mixture is start with the screw turned in all the way. Now back it out three and a half turns. Start the engine. Set the idle speed (looks like 9# and 10# in the drawing until your idle speed is stable. (look at the engine and you want it tick over as smooth as possible set it at this stage by the idle speed, it may idle a bit high at this stage but that’s ok.
With the engine idling away and warm have the filter off the carburettor. Use a playing card is perfect or simular progressively slide the card flat over the hole in the carb. In a perfect word you should get just past ¾ covered before the engine idle speed falls.
If it gets faster and faster as you slide the card over the mixture is the mixture is too lean so turn the idle mixture screw in.
As you get better and closer to the correct point the idle speed will get faster so as you get there correct the idle speed each time. If you don’t the carb sucks more air than at idle and will start drawing fuel from the next jet up from idle.
But I think get a timing gauge, a hand held tachometer, and a vacuum gauge and it will be a cake walk.
PM me if you need help or youtube is you friend.
Cheers Phil
