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I'm not sure what the PMS means but if they are 78 carbs the Air screw starts at 1.5 turns out. It may need a bit either way to be right.
In the carb guide is a chart showing all the year carbs and the stock setting. All the jets needles, air screw and float levels.
It also tells how to ID your carbs. www.amckayltd.com/carbguide.pdf
Leo
That 2 1/4 setting is appropriate only if you have stock exhaust with stock air box, and stock air filters (which seems to be rare these days). Also that is the setting for #27.5 pilot jet. If you have a different size pilot jet, then the mixture screw setting could be quite different.
In 78 they made a bunch of changes. I don't recall engine number this happened. The early 78's had the electricals like the 77, I think they still used the 76-77 carb set. The later 78 used the 78-79 carb set.
On the chart I made up is about the same as the carb guide. It just list the Early 78 and late 78.
The early using the 76-77 carbs will have the 4M1 needle and Z8 jet. The 78-79 use the 502 needle and Z2 jet.
If this leads to confusion, Sorry, Blame Yamaha for making changes mid year.
Leo
Mikuni BS38s, all stock jets & air boxes, PMS set at 21/4 turns out from lightly bottomed, cleaned, fuel levels set, bench sync & running sync with carbtune.
Only things not stock are the T110 pattern mufflers.