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ZS Carb Bypass valve adjustment

To: spitfires@autox.team.net
Subject: ZS Carb Bypass valve adjustment
From: Atwell Haines <carbuff@nac.net>
Date: Thu, 21 Jan 1999 12:26:53 -0500
Hi, all you Zenith Stromberg mavens out there.

During the summer, I noticed that my idle speed would increase 300 - 500
RPM when the engine got _thoroughly_ warm.  This resulted in a lot of
difficulty and frustration in trying to set the mixture and idle speed.

During this time I had to replace the carb with another used one.   The
errant idle symptom was exactly the same with both carbs.  Note: the
replacement carb was rebuilt by me, but I moved the previously
reconditioned bypass valve assy. to the new carb.

Now that the ambient temperature is a lot cooler and the engine temp is
'riding on the thermostat', the idle speed and mixture have been
rock-solid.  The problem returned the other day when a warm spell hit the
area, though.

Should I adjust the bypass valve in an attempt to fix this (admittedly not
very critical) problem?  An adjustment procedure is detailed in the Bentley
manual for my 1500, but my Haynes carb manual says that the bypass valve
should NOT be adjusted, only replaced.

(BTW I have read the VTR web article on adjusting the temperature
compensator, but this does not seem to be fitted to the 150 CDE ZS carb.)

TIA


Atwell Haines
'79 Spitfire  FM96062 UO
Succasunna, NJ USA




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