2X4 carb linkage adjustment

I recently got my car running. I'm running an SBC & two AFBs with progressive linkage. I set up the linkage so both carbs would be open at WOT. Now I realize that I can go up to 4500 RPM before the second carb is activated. I really don't know what RPM I want the secondary carb to come in at. Any suggestions? Thanks in advance, Rod

 

It doesn't have anything to do with RPM. With progressive linkage set up right there is a 2:1 difference between the two carbs so the secondary ends up full open the same time as the primary but doesn't start opening till the primary is midway there. You would do most driving with the primary, only using the secondary when the pedal hits the floor.

 

Please tell me / show what exact intake manifold you are running. Progressive operation of the 2 carbs on most if not all 2x4 intakes I have seen will result in mixture starvation & poor flow to half of the cylinders until both ends are open equally.

 

X2 on this. Guess I've led a sheltered life, but most of my street vacuum secondary 2x4 setups run both carbs primaries on straight linkage and depended upon the vacuum secondaries to take care of themselves when the engine needed the additional WOT airflow.

jack vines

 

Eggzactly... and, ditto for the MANY mechanical secondary carb setups I have run myself on the street and race track or the many, many setups I have done for many customers over the past 38 years. If the motor can't handle the gradual opening of the primary bores together & then the secondaries MAYBE the carbs are too big?? Just my opinion...

 

Thanks guys for the response. I'm running an Eldelbrock C26 intake with two ABFs. I've seen some comments on running straight linkage but was hesitant. Before I got the car running I set the linkage so at WOT both carbs were fully open. I guess I did right, although the fuel starvation thing is kind of bugging me. Thanks again, Rod