[DanEC]

I have the Ford dual quad intake with Holleys and I suspect it's not the secondary barrels that are coming in so strong - but the primary barrels on the rear carb. I have a zip tie tail on my rear secondaries shaft to let me know if I managed to open them on a drive. I too have the really strong boot in the back upon giving it some throttle, but based on the degree of throttle opening and the fact later I often find my secondaries never opened, realize it was the primaries on the rear carb kicking in at about 30% and more throttle.

If the secondaries are properly adjusted on a Holley you really won't experience much of a boot or jump as they open as they should open gradually as throttle increases and vacuum drops.

You might play around with the linkage adjustments a little and you may be able to fine tune the coordination between the front and rear primaries a little to bring them in a little sooner and less dramatically. I don't mind the boot in the back on mine, but it definitely gets your attention.