> Early TR6's (and probably 250's) had both a vacuum advance and a vacuum
> retard on the distributor.
I've heard the opinion voiced that only TR250 has this setup. Do you know for a
fact that early TR6 had it (and it's not just a mistake in the manuals) ?
> They also had some sort of little valve on the throttle linkage that either
> switched or closed off one of the vacuum hoses when the throttle was in a
> certain position.
>
> (maybe fully closed . . foot off the pedal)
Right. The switch simulated the retard port found on later carbs ... when the
throttle was against the idle stop, the valve opened and applied manifold vacuum
to the retard capsule.
> Anyone care to share how all that sort of stuff was supposed to work and
> what the effects are of not having it working correctly?
The vacuum advance worked the same as the earlier (and PI) cars, advancing the
spark under partial load for optimum combustion efficiency. Not having it
working will result in somewhat poorer fuel mileage, slightly poorer
part-throttle throttle response, and possibly a slight increase in overheating
tendencies.
All of which of course were standard on later US-spec TR6 without the advance.
The retard only comes into play with the throttle closed (as above), and was
intended to reduce emissions at idle. If it's not working, the timing at idle
will be affected (obviously), and should be set to the "static" spec (10 BTDC as
I recall) instead of 4 ATDC. With the later carbs, it may be impossible to get
the idle rpm low enough, but might be OK on the early ones. Not having the
retard will also reduce the tendency to overheat at idle.
HTH
Randall
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