Laura,
You're correct. The HS4 SU carb is the closest to what
the Hitachi on the Datsun Roadster's are.
One thing that originally confused me is when someone
made a tuning reference to "one flat". Well, they meant
1/6 of a turn. The British SU carb has a hex sided mixture
adjustement on it. With "six sides" or "six flat" you could
call off "two flats" meaning two/six of a turn. Rather than
just saying, screw in 1/3 of a turn.
Back to the Hitachi carb on the Datsun, the bottom mixture
screw is round. On SOME (most?) carbs is a little bump so
you can keep track of how much you have turned the mixture
know in and out.
One thing I recommend all roadster owners to do, is figure
out where the bottom of the jet it. Have a friend slowly pull
the choke cable, and slide it back in. Watch, and feel,
how the jet slides up (normal mixture), and down (choke
pulled... jet drops down, providing a rich mixture).
One common problem is the jet gets gummed up and may stick,
a little tap on the bottom of the jet will pop it back
into place. Every so often my engine will be running really
rough at idle, due to a jet sticking. Pop the hood, reach
in a just little tap the jet... pops back into place,
and viola smooth idle. Usually I make a mental note to
clean the carbs on the next weekend.
Cheers,
Tom
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