> To date,
> I can find nothing explaining the function and purpose of
> this device.
Check out
http://www.mv.com/ipusers/last/emissions/booklet.pdf
It has a good description.
> It would appear that it is intended to change
> the vacuum conditions between hot and cold operation.
Exactly. When the engine starts to overheat (shown by the radiator being
above the water thermostat set point, don't recall the exact temperature
offhand), the TVS blocks vacuum to the vacuum retard. This has the effect
of advancing the timing at idle, from 4 ATDC to around 10 BTDC, and also
raising idle rpm considerably. The combination helps to cool the engine and
prevent boiling over; but only at idle. During cruise (or acceleration),
the vacuum retard port doesn't provide vacuum anyway, so the TVS has no
effect (and there is no vacuum retard cold or hot).
> I have
> kept the vacuum lines the way they were when I purchased the
> car. The vacuum retard unit is an open connection to the two
> vacuum connections adjacent to the bypass valves on each carb
> when the thermostatic switch when cold.
This is not correct. The vacuum retard port exits only one carb, on the
bottom, from the flange next to the manifold. The hole into the carb bore
is right next to the throttle plate, such that the throttle plate actually
crosses the hole as the throttle is opened (hence the ported effect).
I believe the port adjacent to the bypass valve on both carbs is the purge
line for the carbon canister; unless perhaps you have the bypass valve with
the external vacuum line.
> The fourth
> connection on the thermostatic switch is plugged.
Should be only 3 ports on the TVS, I believe. Sounds like someone has
changed it as well.
> The car has always seemed under-powered and I have
> properly checked and rechecked the timing, but this is done
> with the vacuum retard disconnected.
Where the timing is given as 4 ATDC, that value is only with the retard
CONNECTED and FUNCTIONAL. The instructions that say to disconnect the vacuum
unit when setting timing are NOT correct for US models with the retard.
If you are setting the timing with the retard disconnected (broken, disabled
by TVS), then you should use the "static" timing value, which ISTR is either
10 BTDC or 12 BTDC (probably depending on year).
Randall
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