<VV> Carb Balance < 2000rpm

[Smitty]

From: Kenneth Schifftner <scrubbr at ix.netcom.com>

Why the engine is revved further is not to maintain balance it is to make 
certain that the right carburetor is favored (higher draft than the left) 
that helps actuate the vacuum advance, etc..  GM only allowed for one 
complete turn of the link on the left carb so it is easy to be one turn off. 
I made an adjuster for the left carb and wrote an article about it in the 
NJACE newsletter.  With that homemade adjuster, the right carb can be 
favored more accurately.  It seems like at higher revs the balance tube has 
greater effect.  Really, drivability is what matters.
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Smitty Says;  I have no axe to grind except to correct misconceptions.  I 
still see that there are staunch advocates of adjusting carb match at 
elevated speeds.  One hard fast fact that I wish everyone should consider is 
that the throttle plate is closed at idle and the engine is getting its fuel 
from the "fuel/air" slot inside the throttle bore where a tiny Ventura is 
formed at the little cut out in the edge of the plate.  Also in the bore 
there is another slot which is horizontal which is connected to the upright 
tube on the outside of the carb.  This is either plugged or goes to the Vac 
Advance.  The edge of the plate is below the slot at idle.  At approximately 
700 rpm the edge of the plate moves above the slot exposing it to the vacuum 
under the plate.  That is when the vac adv is activated.  All positioning of 
the vac adv from that point on is controlled by the engine demand and 
throttle position.  I don't think adjusting the left carb link one turn more 
or less would make a visible difference on a tachometer or vacuum gage at 
2000 rpm.  It might be visible at idle.  YMMV