[My427stang]

I run an 850 Double Pumper with a single plane on my 427, I agree it sounds like you are a little on the rich side. I'll tell you my setup, but then play from there

80 in front / 88 in back
4.5 Powervalve in front / none in back

If I were to run 2 powervalves, I'd go 80/82 F/B

I'd start at that whatever matches your setup above, basically, 82 in front and then decide if you are running a powervalve in back or not, and pick the backs accordingly.

By the way, blocking a rear powervalve is OK, but not a front one. Its there so you can get enrighment at low vacuum, but still cruise with some sort of efficiency

Sounds to me that you are not only possibly overjetted, but maybe you have a bad or incorrect powervalve too. Take a vacuum gauge and see what yours has for vacuum at idle. Pic a powervalve 1.5-2 lower. SO if it idles at 8, go 6.0, however, I wouldnt go any higher in number than 8.5 or so, it'll open too easy.

The advice to go to 2.5 probably isnt good for a street driver, thats good for drag racing, but you are telling the carb to wait to enrigh until its flat out open throttle, you'll end up with a low end surge or hesitation. Or worse you'll have to run such big jets, you'll defeat what you are trying to do

Remember, pick the same PV and almost square jet it, little more in back, or block the rear PV and bump up the rear jets.