Don---Champion N12YC plugs are a good choice for most of the TR6
engines. They run a bit hotter than the 9's and this will help keep them
cleaner.
There were/are several types of ZS carbs. The early years saw BOTH the
non-adjustable needle style with a "fixed" jet, and the non-adjustable
needle with the adjustable jet. (Moving the jet gives the same mixture
change as moving the needle the opposite way) Later models had
adjustable needles, with fixed jets. If your carbs are fixed in both
jet and needle, there is little you can do so far as adjustments to the
fuel/air mix. You could TRY lowering the float levels, but not below the
lowest recommended setting, per the Repair Manuals. (.750 is about as
low as one can go)
We'll assume also that the air filters are clean, and permit maximum air
flow.
Be checked to see if black smoke comes out the tail pipe when you start
off or change gears, to help verify the rich mix you suspect. If so, you
may only need a pair of new needles and/or jets. A close inspection of
these parts will reveal wear.
When other parts of carbs wear out, it's usually found that too much
air enters.
It's also possible that the stumbling you experience is not carb
related.
Dick
'73
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