Subject: [TR] TR4A - Balancing Carbs Oddity

From: "G.D. Huggins" <[email-masked]>
Date: Tue, 4 Jun 2013 17:06:12 -0500

Greetings All,

I've recently found myself with some free time, and am looking into those low
priority items on my punch list.
First up is trying to get my engine to purr, as I've always had a rough idle,
with the RPM vacillating over a range of roughly 125, but smooths out while
driving.

I believe the issue might be indicated by something odd with my carbs (SU
HS6), which I had rebuilt by Paltech.
Here's the scenario..

I am using a Uni-Syn tool to balance the air flow (main idle).
The weird thing is that I achieve balance with the front carb's screw not
touching at all (therefore the throttle is not opened at all), and the rear
carb's screw is engaged (thus opening the throttle).
If this is correct, it means I am getting air flow balance from one carb
completely closed, and the other partially opened, which should not happen.

I'm planning on checking for a vacuum leak, and hoping I find one.
Is there anything else I could look for?

Maybe the throttle in the front carb is NOT closing all the way, even though
the idle screw is not engaged?
Maybe the cylinders aren't creating an equal amount of vacuum?

Thanks in advance!!

Cheers,

Guy D. Huggins
1965 Triumph TR4A
CTC 63569LO

Online project diary at http://www.genfiniti.com/triumph

** [email-masked] **

Archive: http://www.team.net/archive

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From: "Greg Lemon" <[email-masked]>
Date: Tue, 4 Jun 2013 18:51:33 -0500

First guess is one throttle disc is not centered (the one on which the screw 
is all the way in of course) or there is a leak in the throttle shaft area 
(should be it properly rebuilt) or the linkage is hanging up and it won't 
let the throttle close all the way, if you push the shaft the direction that 
closes the throttle on the suspect carb end does it slow down?

Good Luck,

Greg Lemon

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From: [email-masked]
Date: Wed, 5 Jun 2013 07:51:13 -0400 (EDT)

The reason is it isn't completely closed afterall.  As mentioned, the disc 
may not be centered.  But also remember you have to disconnect the linkages 
from each other so they may move independently.  If the tie linkages are 
still connected adjusting one set screw will open both throttles.

But you probably knew that.

Dave