Just to add to the database, I've noticed the same thing when using
a Unisyn on my Maserati. Putting the Uni-syn on the center carb would
make the engine really want to stall. Putting the Uni-syn on either of
the other two carburettors would have less of a tendency to do this.
Putting the uni-syn on either throat of any given carb had about
the same effect. From this last piece of data I would assume that
this might indicate a mis-set float level. If it was anything else,
two throats on the same carb could very well have different effects,
and I didn't see that.
My guess for the mechanism is that it indicates a float level that is
too high. The unisyn will increase vacuum in the carb that it is
put against. The fuel in the bowl will be under normal atmospheric
pressure. Thus it would be possible for fuel to just start squirting
into the engine if the float level is too high (the seat acts kind of
like a drinking straw).
Of course, you may be experiencing the same symptoms in your LBC for
completely different reasons. I would check float levels anyway, though.
Joe
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