Decel valve gasket

[Ann and Tim Buja <buja@domain.elided>]

Joe Pawlak and I have been having problems with getting the idle mixture
and speed set correctly on our 1973 Stags.  We noticed that the gasket
for the decel bypass valve has an opening between the two ports.  This
allows allows a small amount of air to bypass the throttle plate even
when the decel bypass valve is closed.

Is there any reason why there must be an opening between the ports on
the decel bypass valve?  The passage can be seen as a figure-8 opening
in the gasket (p/n 517767) on page 02-41 of the Stag parts catalog.
The decel valve is an emissions control device to prevent an overrich
mixture caused by extrememly high manifold vacuum on high rpm overrun.
It opens to allow additional fuel/air mixture to flow around the
throttle plate when manifold vacuum exceeds its set point.

Both Joe and I have cut new gaskets to seal the opening between the
two ports.  This modification has significantly reduced the idle
speed to the point where the idle speed screws can now control the
idle speed down to around 500-600 rpm.  Previously, we couldn't get
the idle speed to go below 1100-1300 unless we significantly retarded
the timing beyond the 4ATDC setting, with adverse effects on
performance.  The decel bypass valve diaphragms are good, and the
internal spring has been set so that the valve opens on overrun but
closes to return the idle below 1800 rpm.

Tim Buja - Rockford, Illinois, USA - 80 TR8, 73 Stag, 72 TR6