William---There are lots of different explanations on what the "vacuum
retard" does for emissions. Here's mine..
Retarding the ignition timing during engine deceleration and idling
speeds is said to reduce an exhaut emission, labelled NOx. The Truimph
Six engine accomplishes this by connecting a vacuum line from a port on
the engine side of the throttle plate. It is here so that there is
vacuum ONLY when the throttle is closed. (As the throttle is opened this
vacuum disappears, and the ignition timing is under the control of the
centrifugal advance, inside the distributor.)
There is another, earlier method of vacuum retard, and has to do with
what look like a trumpet valve, located at the end of the throttle
linkage. When the throttle linkage is relaxed, this valve supplies
vacuum to the ignition retard on one side of the early distributor.
While it did what it was supposed to do, there was no method of
automatically interrupting the retard, unless one sped up the engine
thru the accelerator pedal. This led to a re-design:
A thermostatic switch was placed into the top radiator hose. The vacuum
(retard) line was connected to this switch. When the coolant temperature
would rise to a certain point, this switch would kick in, and the vacuum
to the distributor retard would be blocked off. This causes the
distributor to advance its timing, which also increases the idle speed.
The coolant temperature would then be reduced to the capacity of the
cooling system. NOx reduction was temporarily put aside.
Your question as to whether your vacuum retard is really "doing
anything" could be answered "yes," provided it retards the timing only
when the throttle is closed. It is a waste of fuel to have the timing
retarded at any other time. Operating with a vacuum retard without the
temperature compensator switch in operation leads to overheating at
engine idle, and this is what you seem to be up against. It would be
best to block off the retard line in this case, and set the timing to 12
deg. BTDC. (Less, if the engine pings)
Dick
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