Jay---Something seems backwards in the drawing or source that shows the
retard vacuum coming from the 'front' carb. The theory you are looking
for here is that you want the vacuum source that retards ignition
advance to be connected to a port that sees vacuum only when the
throttle (plate) is closed. This would be the BACK carb at the bottom.
There is a drilling between the throttle plate and the intake manifold
that goes thru to a tube that extends out the bottom of the carb. A
vacuum line on this tube conected to the retard pot on the distributor
will retard the timing ONLY when the throttle is closed, as desired for
some of the emission controls. (NOx)
When the throttle opens, normal mechanical ignition advance takes place
and there is no penalty in timing, as there is no vacuum present at this
port to retard the timing.
Truimph really did get this one as close to right as possible without
electronic controls, in satisfying the Clean Air Research Board.
More on emissions later, for those interested in such things...
Dick Taylor
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