You’re exactly right Ryan. On the progressive linkages the pickup point for the linkage on the secondary carb(s) is closer to the butterfly shaft than it is on the primary carburetor . This causes the secondary carb to open fast than the primary carb. Most manuals on tri-power and dual quads recommend adjusting the linkage to that both carbs reach WOT at the same time.


As long as the carbs were easy to get to while they were on the bench, I set both pairs up so that either carb could be used as either a primary or secondary carb. That was basically just putting the stud for the secondary bracket on both carbs (blue arrow). You can see how much difference there is between where the linkage picks up on the primary carb (top hole) and where the stud is on the secondary carb.


While setting up the carbs the way the manual says is great for racing, most of my driving is Interstate miles. I’ve found in real life on a street car the secondary carbs usually come in too quickly for my taste. I usually set it up so that the secondarys start opening at 80 MPH on a flat stretch of road. The rear carb never really reaches WOT but it’s close enough you never notice it

In the case of the 57 Plymouth the throttle rod actually pushes instead of pulls. That being the case the rod connects to the lower part of the throttle arm (where the red arrow is).

The stud I put in on the carbs for the secondary bracket will still serve a purpose on the carb that is used as the primary…..it will now become where the cruise control linkage connects



Cad AFB P 2 by M Patterson, on Flickr


Jerry, all the ones I've seen (including the factory 409 cars) have had the stop at the front. What you are saying makes sense and I've wondered if that wasn't the original intent by who ever came up with the design. I actually tried setting it up that way on the Dual Quad 440 I built years ago. I was using the Offenhauser linkage that is designed the same as this only the bracket on the front carb was cast aluminum. The problem I found in doing it that way was that the length between the holes in the bracket was too short. When it was properly adjusted to activate the front carb, when the throttle is released the stop would contact the front of the bracket too soon and hold the rear carb open.



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