This may seem fundamental, but should the vacuum secondaries on the double-pump Holley open when I mash the throttle sitting in the driveway, or only under load? I know that the solid lifter engine on the LT-1 generates a little less vacuum, but what else could cause this "problem" if it is indeed that?

Vac. secondary's won't open sitting in the driveway, have to be under a load, don't DP's have mech. secondary's.

The secondaries will open when you floor it no matter where you are. Same on all carbs, thats what gives you that extra go power.

I beg to differ, unless Sportive is free winding the motor to the moon he should not be getting enough of a vac. signal from one of the primary venturis to open the secondary's, according to the holley book they usually won't open unless under a load, if Sport has a double pumper they he should have mech. linkage and if they are not opening there is a linkage problem.

It IS a Holley double-pump, but it has vacuum secondaries, and no, they don't open when I hit the loud pedal sitting in the driveway. Should I change it out to a mechanical setup? Is that doable?

Any DPer I've ever seen has had Mech. secondaries,let me get this straight, it has a excl.pump on the left front corner float bowl and one on the right rear corner float bowl, and if thats the case when
the rear excl. pump comes into play then gas puddles on the secondary throttle blades till the vac. diaphram pulls them open, interesting, never seen a DPer vac.sec. carb before.

anips is correct on the DP deal. All DP Holleys are mechanical secondaries...the secondary linkage is what pumps the pump.

But...on the vac. secondaries not opening, maybe not...
If you floor the carb for about 5-10 seconds, the secondaries will/should start to open. If you apply throttle slowly until you are almost wide open, they will start to open.
If, however, you just "goose" it for a couple of seconds, they will not. The carb has to build vac. in the diaphragm before it will open.

Sportivo...could you take a photo of this carb?...it sounds interesting.

Thanks Apple for helping clear the vac secondary thing up, if you are going to load a sb chev by free winding at WOT for 10 seconds make sure you have your safety equiptment on, i.e. ear plugs, Kevlar, flak jacket.

ok, ok...maybe 10 secs might be a bit too much...i never were any gud at numbers!

Joel, you did damn good, the point is you can't ck the secondaries by goosin the throttle in the driveway.