I've used a Unisyn for over 40 years and there are some tricks and a
learning curve to it. The whole deal with the Unisyn is to develop a
"touch", slowly bringing the two carbs together until they match.
The SU reactions that you are experiencing are not at all unusual for a
badly out of adjustment set of SU's. Might not be anything else wrong with
them or your car. Most other things have been covered in the posts here
except for the answer to the one specific question that you asked regarding
having to hold the idle up to use the Unisyn on one of the carbs and were
you missing knowing something about the Unisyn. Without actually seeing your
setup in person, I feel that this could be the most likely cause of the
issue that you are experiencing with your SU's. Before you tear in to all
the other suggestions, try the following:
The Unisyn has a "dial" adjustment in its throat. It is a little adjustable
disc dial. Turn the disc dial one way and it lets more air in. Turn it the
other way and it lets less air in. You'll see the air gap increase and
decrease ( a little) in the throat of the Unisyn as you adjust this disc
dial. With carbs so badly out of sync, as yours undoubtly are, you will have
to start with a dissimilar adjustment of this "dial" for each carb. Adjust
the Unisyn for each carb so that the engine stays running, sllllooooowly
adjust the idle speed bringing them into a state where both carbs allow the
engine to run with the Unisyn in place. Unless the mixture adjustment is
really out of adjustment bad or unless you have a mechanical issue, this
should be fairly easy to accomplish. If the mixture is that badly out
causing a no idle condition on one of the carbs, this will have to be
corrected first. Usually I'll turn the mixture in till it misses and the
idle roughens, and then out until it smoothes out enough to stay running.
I've made some B's, Sprigets, Tri**phs and other similar twin SU vehicles
run smoother than some thought possible with a Unisyn (and everything else
being ship-shape too). Check all the other stuff that the other listers have
mentioned too if the Unisyn used this way doesn't do the job - but I'd bet
it is not as complicated as all that. SU's are pretty forgiving and usually
learning how to use the Unisyn properly will make you an English car/SU ace!
This is just the most basic instruction and working with it you will further
self-learn the fine details. And, if anybody else can help further and add
to this, have at it!
Good luck!
Jerry Erbesfield
Was 73 Black Beauty B
Now C-5 Black Beauty Vette roadster
E-mail: jerbesfield@mindspring.com
Website: http://jerbesfield.home.mindspring.com
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