X2...I Have never had a response problem with a DP off idle.After owning a few vacume secondarys i find them very lazy from a performance point of view.Fine for a daily driver.
In my combination with a vacuum secondary Holley the secondaries never opened fast enough even with the lightest spring in the can. The DP pulls hard from any rpm. Some of the better professional carb tuners can put what seem to be outrageously large DP carbs on small motors and they are very responsive. They go to the point of dialing in air bleeds, emulsion tubes, etc. Or you can buy a set of Weber Power Plates that add an extra low rpm circuit for more tunability.
Wow, I am out of town and not responding or reading as much as normal...lots to say here, from my experience with this carb. Mine does NOT have a secondary power valve, so maybe that is why I am needing more jet in the secondaries. Mine does too! It lights right up when I hit it. I have the squirters set to squirt as soon as there is any movement, and it has no bog whatsoever now that I riched up the jets to correct the lean I had. The remaining lean is very minor, and only a "car person" would even notice it, so I think another jet or 2 will fix it. It is only after the secondaries are open and the rpms are climbing and the car is asking for more fuel, then I can feel a little hiccupping where it is leaning out. I can feel the squirters working when the secondaries open, but after that fuel is burned, I feel it lean out a bit. I don't have the experience at this point to add to all of the other discussions, so if I didn't address what you said, that just means I am sitting back and reading and "taking it all in"!
I have never used a PV out back either. Never really even heard of it. That is apparently, if I understand correctly, why the rear jets are always several sizes higher than the fronts. This is very interesting to me as I have several primary blocks laying around. Would someone who knows, respond about if it's recommended to use a regular primary block out back to get a PV in there... If so, should you just abandon the idle circuit on the block, or just settle for 4 corner idle? Would you use the same PV size out back as up front? Seems all this would make a really tight running secondary system. Tight, as in good and crisp. Then you would probably run the same jets out back too.
Unless the carb, or carbs are mounted sideways, Do not use a power valve on the rear. They do not make power valve extensions. This is why on a hard leaving car you have to run jet extensions. The front metering blocks can be run on the rear, If you know how to set up the emulsion bleeds. Otherwise the fuel curve can be off. But they will work. As far as double pumpers on the street, Mine is a 1000+ cfm (actually wet flowed at 1150 cfm) It gets 16+ mpg as long as you keep off the gas. A Holley is the most versatile carb out there as long as you take time to tune.
There is a Holley kit to place a "primary" type block on the rear of the carb. If you are running a double pumper it makes it a lot easier to get the mixtures right without dumping raw fuel down your bores when cruising with the secondaries open. I don't suppose anyone here cruises fast enough to have the secondaries open when not in "full acceleration" mode.....
