In a message dated 11/26/2011 6:54:31 PM Central Standard Time,
drew at graybealdesign.com writes:
> What seems to make the difference
> now is removing the vacuum retard hose and plugging it. I don't have a
> timing
> light so I can't be sure it's just timing and not a vacuum leak in the
> distributor, but hose on...it runs bad...hose off...it runs good. Do I
> need a
> new distributor? Can I fix the old one? Is this really the problem?
If connecting the vacuum retard line makes the idle increase and removing
it causes it to drop then I suspect you are actually connecting it to the
vacuum advance module (if you car is so equipped). It's easy to get confused
and the best way to determine which is which is trial and error.
As I recall the 71 models still had the advance module but it was ledt
unused. I reconnected mine as it tends to imprrove fuel economy (marginally).
But you need the vacuum advance port on the carburettor which was not
present on the 71 model carbs. But 74 and later carbs did have that port and
it
was used for the EGR valve.
The vacuum retard system acts to stabilize the idle speed. As the idle
speed picks up the vacuum will increase. This will retard the timing reducing
the idle speed. As the speed reduces the vacuum will decrease advancing the
timing to increase idle speed. Pretty clever. But this was important for
cars required to meet emissions. Since these cars were tuned quite lean at
idle maintaining a constant idle speed over varying temperatures was
problematic and meeting emissions over a wide idle speed band was difficult.
Since
the retard module is feed from a special port on the carb that provided
vacuum only when the throttle was closed it had no effect on normal driving.
Dave
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