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TR6 Thermostatic Vacuum Switch

To: Triumph list <triumphs@autox.team.net>
Subject: TR6 Thermostatic Vacuum Switch
From: Tomislav Marincic <TomAndKate@compuserve.com>
Date: Sun, 21 Mar 1999 15:43:21 -0500
Cc: Trevor <tjordan@vic.bigpond.net.au>
        Trevor,

        RE:"I do not even know what the bypass valve bypasses."

        The bypass valve found on most CD2-SE Zenith-Strombergs
is meant to bypass the throttle plate when it is closed and the engine is
on what the Brits call "overrun" and what I suspect many of us in the US
might think of as "engine braking". When manifold vacuum ("depression")
gets too high, the valve allows a small amount of air/fuel mixture past
the closed throttle plate, thus limiting the vacuum and consequently, the 
high emissions produced in this situation. 

        The post-'68 US-spec SU
carbs achieved this effect with a comical poppet valve device directly on
the throttle butterfly. At wide open throttle, this valve blocked
considerable
airflow into the engine. It also presented a damage hazard if it ever came
loose during operation.


        Good luck with your TVS riddle.

        Best Regards,

        Tom Marincic
        

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