Quote:

so if you floor it in park or netural the outboards will not open? what is it about the vacumm while driving or sitting still that makes them open? does a 4bbl open under the same conditions?


(From a few post before..)
(RR dude)- My outer carbs don't always seem to be kicking in. I have 10 lbs vacumn. What color springs should I have in the outboards. I don't understand why vacumn would't have anything to do with them opening when you have vacumn to them.

(LEE446)- If manifold vac was used, the end carbs would be wide open at idle! The vacuum that operates the end carbs is generated by airflow through the center carb venturi's. When airflow is high, as in W.O.T,on the center, a high vac signal is generated and sent to the end carbs via the vac hoses that hook up to the center carb. End carbs also have a "Kill Bleed" that is a tiny hole in the venturi that bleeds off some of the vac signal so that the carbs don't open too soon. 340 carbs have a bigger kill bleed hole so they would open slower if used on a 440 car.

(macmic87) the kill bleed size determine at what rpm the secondaries will start to open and the springs regulate how fast they open. small block carbs have larger kill bleeds to have the carbs open at a higher rpm.

(Moper) I would start with stock plain. The next faster is purple, then tall yellow, then short yellow IIRC. I have never had to use more than the tall yellow in a 6bbl. You should never feel a bog as they open. As noted, they run on a vacuum signal generated by airflow thru the center carb just like a VS 4bbl uses the airflow from the primary half. Not the piston produced vacuum you're thinking of.

HOPE THIS HELPS.....Might save a few others from typing this again

A True Hybrid: Burns Gas AND Rubber!