I am rebuilding another one of these for a friend of mine and got to thinking about something during disassembly and checking the butterfly shafts. When these things were run back in NASCAR in the 55/56 seasons, were the secondaries always vacuum? Did the engine builders ever modify these to be mechanically opened secondaries? Just wondering - thought it would be a trick way to put one back together if one of my buddies was going to use it for vintage racing.

Daniel Jessup

Lancaster, California

aka "The Hot Rod Reverend"
check out the 1955 Ford Fairlane build at www.hotrodreverend.com

Dan, most of us just stick a screw in the slot of the linkage. If the vacuum is working correctly there is little or nothing to be gained by a mechanical setup.

Frank/Rebop

Bristol, In ( by Elkhart) 

I have run the dual quads on my Bird both ways. More drivable without the screw and times seem to be about the same either way. Feels stronger with the screw though.

I have the best overall results with the Teapot secondaries being activated with a vacuum signal rather than with some form of mechanical linkage. Mechanical secondaries if activated with the rpms being too low will provide inadequate air flow through the carbs for them to provide any performance benefits.  Coughing and/or backfiring through the carbs is a common symptom of what happens when the secondaries are converted to mechanical activation without the secondary side fuel system being made much richer in which to compensate.

The model 4000 Holleys (Teapots) use the same vacuum secondary springs as the model 4150/4160 Holleys which makes tuning the secondaries much easier on the dual quad setups.  Using either the long yellow or short yellow springs from the Holley spring kits are a good starting point for the dual quad Teapots.  An equalizer tube or connecting line between the secondary pots will also allow both carbs to open more equally.  When the seconardaries are opening correctly, it will be a smooth transition without any noticeable jerks or bogs taking place.

Lorena, Texas (South of Waco)

In most cases if you can FEEL a difference when the secondaries open, you've got the wrong spring in it. As Ted said, when it's right it's almost imperceptible.

Frank/Rebop

Bristol, In ( by Elkhart) 

thanks fellas, just tinkering with the idea here. Wayne does not have any dual four barrel setups, but he only runs teapots his 55 and 56 Fords, of which he now has 3 and I guess he has appointed me the carb man for his stable... hopefully he hasn't made a bad choice. I guess the proof is in the daily driver"ability" of the carbs I set up for him - the more they go without stumble or leaks I reckon the more he likes it.thanks for the info, I will tuck it away.

Daniel Jessup

Lancaster, California

aka "The Hot Rod Reverend"
check out the 1955 Ford Fairlane build at www.hotrodreverend.com