I'm running a 650dp on mine (10.7:1 351@.060), with the stock 67s in front, a 35 shooter, and a 4.5" pv (if memory serves - may be a 6.5"). A friend with an identical motor except for a 750 vac-sec carb was running 72s up front (at the time, non-adjustable secondaries), so I actually put 72s in when we finished the motor, which ended up being *way* too rich. With the 72s, I'd get a stumble at about 4000 before I opened the secondaries (does anybody else notice a distinct point in pedal travel where the secondaries open on a dp?) which went away when I jetted down up front. Plugs are barely on the lean side of just right right now. I still have a stumble under 2000 rpm, so I'm guessing I need to mess with the shooter or the whole pump cam/diaphragm thing, which I'm not overly eager to do at the moment.
Definitely an interesting topic to me - maybe Don and DV will chime in. At one point I emailed Holley tech, but only got a worthless "every motor is different, blah, blah, blah" response.
JLW
PS - Rob's car (with the 750 on an identical motor) still has bigger jets up front, and doesn't run richer. Combining our vast carb-tuning and fluid dynamics knowledge (which unfortunately, simply proves that multiples of zero are still zero), we came up with a theory as to why that should be:
Given that a 650 will pull less air than a 750 at any RPM, then the vacuum signal at the jets will be bigger for the 650, meaning that a given jet will send more fuel at that RPM on the 650 than on the 750 due to the bigger vacuum signal.
Any chance this is reasonable, or did I just give everyone a good Tuesday laugh?
For what it's worth
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