Rick :
As Dave has correctly pointed out, 1/4" is too far for the "lift the
piston" test. ISTR the correct value is more like 3/32".
However, I believe there's a more fundamental problem : the "lift the
piston" test does not apply to your carbs. The test assumes that you
want the idle mixture to be "max power", but US emissions laws required
that the idle be much leaner, to reduce carbon monoxide emissions. The
limited needle adjustment was also required by US law, to keep people
from doing what you're trying to do !
Sorry I don't know what the correct procedure for your carbs is, but I'd
guess it involves a CO analyzer. If the float level is right, and the
plugs look OK, and you're already max rich, then I think it's safe to
assume that you are already on the rich side of 'correct', and that your
rough idle is most likely ignition. It has to be in top shape to
reliably fire the lean mixture.
Also check for vacuum leaks, especially the subtle ones like leaking
vacuum retard diaphragm or leaking brake booster. I don't recall what
the crankcase ventilation looked like on a 73 TR6, but if it's one of
the ones that tries to pull a vacuum on the crankcase, then a leak
anywhere will cause the idle mixture to go lean, from air sucked through
the crankcase. A defective anti-runon valve (if you have one) could
also be a problem.
Randall
Rick Barnard wrote:
>
> Hi Folks,
> I attempted to adjust the mixture on my ZS 175 CD's tonight. I
> was following the Leyland book, that is, lift the pistons 1/4" and the
> idle dropped and the engine almost died. So that means they are too
> lean. Took my handy Zenith adjustment tool and tried to adjust
> clockwise, BUT both carbs are already at the max adjustment. These
> carbs are only 3 years (6K miles) after a "professional" rebuild.
> I wonder if I have the incorrect needles? The car has a rough
> idle, but seems to run good at speed, and the plug color is normal.
> Any advice appreciated!
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