Geoff---8 deg. ATDC is quite a bit of retard at idle. (Could you have
meant 8 deg. Btdc?) If the retard vacuum line is not influencing (as it
sounds from your message) the timing, then you probably are not getting
the full advance when the timing is all in. Use your timing light again,
and see if it shows near 30 deg. BTDC. If you insist on using the
vacuum retard, be sure the line feeding the distributor originates at
the manifold side of the throttle plate. The port for this line is
usually under the rear carb. It only has vacuum when the throttle is
closed.
You can usually advance the timing more at idle when a performance cam
is in place. Let detonation or pinging be your guide here. 12 deg. BTDC
at idle is not uncommon. (Even more, if you limit the total advance)
Finding the cause of your errant idle still sounds as if there's a bind
somewhere in the linkage. Stock linkage leaves a lot to be desired, and
has a lot of slop in it that can be lessened, with care. Disconnect the
linkage as before, and operate it by hand. Something has to show up.
Dick T.
'73
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