[TR] 61 TR3A SU H6 Carb Issues

Randall tr3driver at ca.rr.com
Wed Oct 17 06:55:32 MDT 2018

> Just wondering...  Q for the crowd at large.... does anyone 
> still use  the little rods in the tops of their carbs for balancing?
> (usually little kits with a jet wrench and etc)

I do, on occasion. My hearing isn't what it used to be, so it's nice to have
a visual check in addition to the "listen to the hiss" method.

Another thing it offers is that you can check how well the throttle plates
track each other when the throttle is opened.  The TR3 style linkage, with
the pedal connected to the front of the front carb, definitely flexes a bit,
causing the synchronization to be off as soon as you step on the pedal.  How
much it flexes may depend on things like how tight the return spring on the
rear carb is, and how rusty the little wavy clamps are that connect the
throttle spindles.  Dave mentioned the lost motion in the later linkages;
here's how you check that, too.

But honestly, I've never been able to tell the difference in how the engine
runs.  Even with the synchronization way off, all I get is a little rougher
idle (bit of a lope, almost like a performance cam).  The engine still runs

No doubt it varies from instrument to instrument, but I was very
disappointed in the Uni-syn clone I got.  The ball was rough, and didn't fit
the tube very well, making it very insensitive unless the tube was
positioned almost horizontal.  And even then you're relying on the carb
faces to both be at the same angle to vertical, which might not be true.
It's in a box somewhere, I haven't tried to use it again.  Even on the
Stags, which make using the "little rods" problematic because the carbs are
on opposite sides of the engine.

IMO there is also a lot to be said for a method that uses something laying
around (a length of old fuel line or heater hose works just fine) as opposed
to a relatively expensive instrument that has to be stored and cared for
(and invariably is in the other shop).  Right now, I'm some 2000 miles away
from my rollaway tool chest, looking at a TR3A that I had originally hoped
to have running this year.  Not gonna happen, but when it does, you can bet
I'm not going to go get that tool!

In a pinch, you can do an adequate job just by sticking your good ear as
close to each carb (but the same distance) as possible.  Many years ago now,
I followed a Spitfire on a club run that was blowing black smoke and
obviously struggling with the hills.  When the group stopped, I mentioned
the black smoke to the driver.  Long story short, I wound up adjusting his
carbs right there in the parking lot, with just my ears and fingers.  He
told me later that it ran better on the way home than it had in years, even
right after a professional tune-up!

-- Randall

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