Don---Tho hardly an expert about such matters, and with no dyno tests to
back it up, I still have some thoughts about this subject. Know that it
comes more from theory, not hard evidence. So....
In order for the CD carb to be used to its best/most power advantage, it
must open far enough for the air valve to expose the smallest diameter
of its needle. This allows the greatest flow of both air and fuel. When
only TWO cylinders pull air across the bridge, there is a third less
displacement to raise the air valve. This could mean that the air valve,
(or air piston) does not come up far enough to take advantage of its
"extra" volume. (Remember the discussion on CFM?)
If an engine is capable of much higher rpms that what most TR's ever
see, then the CFM requirement goes up accordingly. That's when the third
carb can help, even if it means three smaller ones.
If there is an advantage for using the three carb setup, it might come
from not necessarily more air/fuel, but from less fuel fall-out, such as
is the case with PI. In short, better distribution.
Dick Taylor
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