<VV> Syncronizing Carbs

[Smitty]

Smitty Says;  I read a post the other day and immediately started to write a response that could be considered abrasive.  Then I thought , why bother.  Well the bother to me is that if a newbie, or other, that is just starting to grasp the subject, reads it, and believes it then I have done him a disservice by not correcting the information.  The subject was synchronizing carbs and making adjustments at 2000 rpm.  
Nowhere in any GM manual is mention made of adjusting carbs at 2000 rpm.  All references are to making adjustments at idle.  Synchronization is for the purpose of obtaining a smooth idle and no other reason.  Smooth idle is important from a mechanical point of view because you need a strong stable idle to carry the load of dropping the PowerGlide into low gear when the car is stopped.  Oh, it’s nice to have a smooth idle with a stick shift too, but with a PG it is a necessity.  The rpms for a PG are 700 in neutral and 500 in gear.  You can not properly adjust idle air mixture above right at 700 rpm because at that speed the throttle plate is leaving the idle air slot inside the carb throat, leaving the idle circuit inoperative.   All the tweaking of the idle air valve in the world will do nothing for your engine at speeds above 700.  Of course the idle speed screws were matched when you do the initial synchronization at idle.  At 700 they are no linger touching the speed advance cam and screwing with them will only mess up the matched idle speed you have already done.  now there is only one other thing that is adjustable.  That is the linkage.  if you are following the book you have the two carbs disconnected and isolated from one another.  Hopefully held in the idle position with rubber bands or springs or whatever.  You hook up the right carb first.  Then you adjust the little swivel on the left carb link between the cross shaft and the carb to where you can just slip the swivel into the hole in the carb link.  Add one additional turn tighter to make the right carb crack open first to start the vacuum advance.  Now if the engine is turning at 2000 rpm and you screw with that linkage you will destroy that fine adjustment you made at idle
I watched a supposedly guru at a national convention doing a tech session one time.  He jumped through all the wickets to synchronize the carbs on the demo engine and then with a vacuum gage he matched the carbs at 2000 rpm.  I walked away in disgust.