Ashford---If the friend really has the two inch SU carb, it is one of
the easiest to tune. The adjustment that controls the mix is a spring
loaded screw against a lever. Running the screw down lowers the jet,
which richens the mix. This same lever may indirectly have the choke
cable attached to it, as "choking" this carb also lowers the jet, for
starting enrichment.
Note that the jet can be from .040 to as much as .090 below the bridge,
depending on the height of the needle.
This means that another way to change the mixture strength is raise or
lower the needle, by loosening the grub screw on the inside of the air
valve. (Very easy to do) Best tho to set the needle to where it's
undercut, even with the bottom of the air valve, and do the adjusting
with the jet itself, as adjusting this way can be more precise.
For those who have such a carburetor, the Haynes workshop manual on the
SU is indispensible. Easy to read with lots of pictures. My favorite
kind!
Dick
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