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Checking vacuum advance

To: Mark Hooper <mhooper@pixelsystems.com>
Subject: Checking vacuum advance
From: Dave Massey <105671.471@compuserve.com>
Date: Fri, 21 Jun 2002 20:15:45 -0400
Cc: "Triumphs Mailing List (E-mail)" <triumphs@autox.team.net>
Message text written by Mark Hooper
>I have a distributor with only the vacuum advance on my 72 TR6. Last night
while tweaking the carbs a bit, I pulled the vacuum feed off the advancer
just to see what effect the unit had on the idle speed. Apparently none at
all. Is that normal? How should I check this thing? Does sucking on the
pipe
give enough vacuum to see the points mounting plate in the distributor
move?
Is there some way to measure if the advance is working well or poorly, or
is
it simply working or not?
<

Mark, if the vacuum is from a port on the top side of the carb (as it
should) then you will see no change at idle.  This is because this port is
ahead of the throttle plate when the throttle is closed.  It is positioned
in such a way that once the throttle is opened this port will be behind the
plate and will at this time see vacuum.

You can typically create enough vacuum to see the plate move by sucking on
the tube and if you do this while the engine is running you should see the
speed increase.  If it decreases then what you really have is a vacuum
retard (typical if the US cars) and it should be plumbed to a port on the
bottom of the carb that had vacuum only when the throttle is closed.

Cheers

Dave

P.S. NTSC: 525 lines at 60 Hz scan rate, PAL: 625 lines at 50 Hz scan rate.
 Secam: a way to photograph fish.

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