Doug :
The switch in the upper radiator hose disables the vacuum retard when the
engine starts to overheat. One vacuum line runs to the rear carb, the other
to the vacuum retard solenoid on the distributor.
Whether to connect the vacuum retard system at all is your call, it does
theoretically reduce tailpipe emissions when the engine is idling (and is
required by law to be present and functioning, in some areas). With the
system connected and functioning, the switch itself doesn't even reduce
tailpipe emissions (but is still required by law in some areas, as it was
part of the "emission control equipment").
Note that, if you do leave the retard disconnected, there are some other
changes required, like setting the timing to 10-12 BTDC rather than the 4
ATDC specified. You may also have trouble getting the idle speed down.
Randall
>
> I've recently purchased a 73 TR6 that has been garaged for many years. In
> preparation to start it up, I'm doing and replacing all of the recommended
> stuff.
> I've got a question, though, about the thermostatic switch that is placed
> in the top radiator hose. I can see from Bentley's workshop manual that
> there are two vacuum pipes that should be attached to this valve.
> I also can
> see that one should be atached to the rear carb. Due to a PO, however,
> there are no lines attached at the moment.
> Here's my questions:
> 1. what does the switch do and what should the vacuum pipes be
> attached to?
> 2. should these be hooked up to run the car at length? In other words, is
> it mechanically and environmentally correct to fix this?
> Any advice would be greatly appreciated.
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