Mark Stahlke <mstahlke@denver.infi.net> writes:
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The vacuum retard was an emissions related item. With the (broken) switch
bypassed I don't think it's doing anything. That's the real question here.
What is the vacuum retard doing with the switch bypassed? My car runs
cleaner
now than it has in the 2 1/2 years that I've owned it. See my reply in the
ZS
bashing thread. The emissions testing I mentioned was done with the vac.
retard in it's current configuration.
I like breathing clean air too!
Reagards,
Mark
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One advantage you get from the retard module is the idle stabilization
effect. Here's how it works:
When the engine is idling with a fixed throttle position a faster idle
will give you a higher vacuum. With a fixed throttle position,
advancing the timing will cause the idle speed to increase and retarding
the timing will cause the idle speed to decrease. Now the vacuum retard
module will retard the timing more with a higher vacuum. The net result
is that when the idle speed increases, the vacuum will increase and the
timing will be retarded causing the idle speed to decrease. These
effects counteract each other and reach a happy medium resulting in a
fairly constant idle speed.
The retarded timing also reduces emissions. Also note that the source
of vacuum for this module is a port on the underside of the rear
carburetor which only provides vacuum when the throttle is closed.
Just as soon as the gas peddle is pushed the vacuum is removed from the
module and the timing returns to the optimum setting for the car.
In the later cars with the thermatic vacuum switch the vacuum will not
be applied to the module until the engine warms up thus boosting the idle
on a cold engine.
On the cars fitted with the throttle linkage actuated valve the valve will
dump the vacuum as soon as the throttle is pressed giving you a head start
to un-retarded timing.
At least thats what I Think!
Dave Massey, St. Louis, MO, USA
71 TR6, 74 TR6, 78 TR7
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