Subject: [TR] TR4A - Balancing Carbs Oddity

From: Q <[email-masked]>
Date: Wed, 5 Jun 2013 09:12:18 -0700 (PDT)

You may want to check that the pistons did not get swapped from one carb to the other.  While the piston itself is a generic fit part there is a height adjustment at the bottom of the piston, a small brass area if I remember correctly, that sets the stop height of the piston at idle.

I had a set of TR4 carbs come back from the rebuilder in such a condition.  The telltale was that with the engine stopped and the air cleaners off I could see that the gap below the piston was different on the two carbs.  Swapping the pistons made the gaps equal and cured all the strange idle problems I was having.

Edward Hamer
Petaluma CA

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From: [email-masked]
Date: Wed, 5 Jun 2013 13:04:33 -0400 (EDT)

Guy,
 
This is not meant to be insulting but sometimes little obvious things get  
overlooked.....did you slacken the throttle linkage clamps next to both 
carbs to  allow the carbs to work independently of the accelerator shaft?
 
You can't set proper balance if the throttle shaft between both carbs  is 
fastened tight.
 
If you're good on this then try using the front carb as the starting point  
for balancing by turning the idle screw down to raise the idle to a point 
where  you can say you've actually raised the idle by turning the screw.  Set 
 the UniSyn to that flow rate then go the rear carb and set its idle screw 
to  achieve the same Unisyn flow rate.
 
Once you've dialed in a balanced flow rate, tighten the throttle shaft  
clamps, give the throttle a few good blips to settle things down and adjust 
each  idle screw up or down equally to get the desired idle speed.
 
Providing that everything else is "okay", this should balance your  carbs.
 
Chip Krout
Delaware Valley Triumphs, Ltd.
Skippack, PA 
1962 TR4  CT2052L

In a message dated 6/4/2013 6:16:34 P.M. Eastern Daylight Time,  
[email-masked] writes:

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

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