Reply to: RE>Uni-syn for TR6 carbs
Peter, if you look at the mouth of the Stromberg, you'll see a hole above it.
This hole vents the bottom of the diaphram in the carb to the atmosphere.
When you open the throttle on a Stromberg, the increase in airflow through
the carb creates a progressively greater vacuum in the venturi of the carb.
This vacuum is transferred to the top of the diaphram via two holes in the
bottom of the throttle slide, and the atmospheric air pressure underneath the
diaphram lifts the throttle slide.
As the underside of the diaphram is isolated from the vacuum in the venturi
only by the close tolerance of the slide to the body of the carb (that is, it
leaks to vacuum), the underside of the diaphram must be constantly vented to
the atmosphere.
When you slap the Unisyns on the carbs, you cover up the vent hole, and the
underside of the diaphram "leaks down" to the venturi vacuum. With no
atmospheric pressure to hold the slide up, it falls down, closing the
venturi. Consequently, the engine runs slower or may even die.
To make a long story short. Drill a hole in the Unisyn plate that aligns with
the vent. It'll then work fine, provided you adjust the little wheel in the
center properly.
Scott St. Clair
'68 TR250
--------------------------------------
Date: 9/11/95 4:28 PM
To: Scott St. Clair
From: Peter Barrance
Hello everyone:
Got another question for the group. TRF had the Unisyn carb air-flow
meter in stock when I placed my last order, so I decided to order one.
This weekend I had a little time to spend on the time so I pulled off the
air cleaner and tried to check the balance. What I found was that putting the
meter over either carb throat (stock Strombergs) when the car was idling
caused the motor to bog down, more so with the rear carb. The drop in rpm
was noticeable with it over the front carb. I tried different settings for
the
air flow control for the Unisyn, but I couldn't get anything to lift the
float in the meter. The engine slowing effect was less noticeable with the
air
flow control opened up, but still no way to see the float rise. Revving the
motor up (significantly) moved the float up the tube.
I should be able to use this thing to set the idle balance, shouldn't I? If
the presence of the meter has a significant effect on the airflow, I'm not
going to be able to use it to improve the balance.
Anyone know what I'm missing here? I admit to not having spent time trying to
experiment with modifying the meter or anything.
By the way, I have a Unisyn model A. Do these come in different sizes for
diff
erent carb sizes. I have the 175 Strombergs.
Cheers,
Pete
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From: trs@eagle.gsh.jhu.edu (Peter Barrance)
Subject: Uni-syn for TR6 carbs
To: triumphs@autox.team.net
Date: Mon, 11 Sep 1995 18:31:43 -0500 (EDT)
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