what is ideal position of throttle blades at idle ?

[Frank400]

Should they be completely closed and trying to get the idle ok with only bypass air ?  Reason I ask is because if we crack open the throttle blades a little bit with the idle speed screw, there is a smaller portion of the transfer slot "left to work", kind of.  If we close the blades completely and get 100% of the air thru the bypass, a longer portion of the transfer slot is available.  In other words, should we close the blades and rely only on the bypass air for idle ? 

[qjetsrule]

FRANK, A SMALL PORTION OF THE VERTICAL TRANSFER SLOT (.020-.030") SHOULD BE EXPOSED TO MANIFOLD VACUUM (BELOW THROTTLE BLADES).  THIS CIRCUIT NEEDS TO BE ACTIVE AT IDLE TO PREVENT A HESITATION. THE CIRCUIT CANNOT INSTANTLY RESPOND TO OFF IDLE THROTTLE MOVEMENTS. BUT, EXPOSING TOO MUCH OF THE SLOT HAS A NEGATIVE EFFECT ALSO BECAUSE THE TRANSFER CIRCUIT WILL ALREADY BE USED UP, ALSO DECREASING YOUR ACCELERATOR PUMP SHOT AND MAY CAUSE NOZZLE DRIP. THIS ARTICLE HAS A NICE PICTURE. GOOD LUCK

http://www.competitionplus.com/07_15_2004/carburetors.html

[Frank400]

Thanks, great article.  I do know about the transfer slot, maybe it's the way I formulated my question.  In fact, would it be BETTER to completely close the throttle (even remove the idle speed screw !) and go with bypass air alone, EVEN if that means removing the carb many many times to re-drill the bypass holes until the idle speed is right on the money ?  Frank.

[73 Z28]

Frank,
The idle bypass air sizing is to compensate for a larger camshaft, what you can do is, with the carb on the bench, set the throttle blades with the curb idle screw so that a small portion of the transfer slot is exposed, then use the idle mixture screws to get a smooth idle. If the mixture screws cannot be adjusted to give a satisfactory idle, then the idle mixture screw holes need to be enlarged or additional bypass air is needed or both.

Paul

[Frank400]

Thanks !  That is exactly what I wanted to know !  Frank.