I'm not too good on the details because I moved all the vacuum lines to places
of my own design but I think I understand the theory.
That vacuum port is not measuring "venturi vacuum" which would get stronger the
faster the air flows through a venturi. It is supposed to connect to regular
manifold vacuum which is strongest when the throttle is closed and weakest at
wide open throttle. There is one difference - the port is just a hair outside
the throttle plate so that it will have no vacuum when the throttle is
completely closed but it will have normal manifold vacuum at all other times.
Hope this helps (hope it's right)
Ed McGuirk
76 TR6
87 Rx7
88 MR2 Supercharged
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Date: Sat, 23 Jun 2001 13:42:15 -0400
From: "Jay Snavely" <jays@paonline.com>
Subject: vacuum sources and theory
Could someone explain the proper source of the vacuum for the vac retard
unit. All the drawings I have seen for the 1974 TR6 configuration show the
small black vacuum line connected to the bottom of the front carb. I am not
sure where this source is in relation to the throttle plate, but it looks to
be upstream. It seems to me that this vacuum would be minimal at idle, and
increase with throttle opening. It seems to me that this would be opposite
of the desired vacuum for operation of the vacuum retard.
There are also vacuum sources on both carbs connected to the larger, green
vacuum line, and a port on the manifold side which connects to the EGR
valve. What is the vacuum strength in relation to engine speed on these
ports? What is the purpose of the green tube which runs to the TVS?
Is there an explanation on the web somewhere? Thanks for any explanations.
Jay Snavely
74 TR6
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