Well it was the last day at the track this year and my buddy had his Dart Block 427 63' chevy II out for the last time. He finally got his 60' down in the 1.5's and ran 11.02 @ 124.5MPH, not too bad for a street car that gets cruised a couple thousand miles a summer. The problem was that his plugs were showing lean. He was maxed on jetting with 99's in the rear and 91's in the front of his 850 annular mighty demon. His combo looks like this
-Dart block 427 10.5:1 compression
-Brodix 227cc M2 track 1's
-268/268@.050 .575/.575 lift on a 108 solid F/T cam
-super vic
-1 3/4" headers
-tremec 5 speed.
Hes running a 130gph mechenical carter fuel pump. Hes thinking hes running out of carb but I suppose its also possible its his fuel pump. Maybe both. The only reason its not obviously his fuel pump is because its not nosing over at all. Hes thinking of going with a 1,000CFM race demon and his 172 GPH carter he has laying around. Any suggestions or ideas?

That big mechanical pump needs some big inlet line too. I believe they come with a -10 fitting on the inlet side. I would run a short length of -10 forward of the pump (so fuel is being pushed toward the pump on launch) and 1/2" back to the tank.

I would do some testing (like with a fuel pressure gauge and an O2 sensor) before zeroing in the the carb and jetting.

JMO

hmm 850 cfm is kinda small for the 427.
a 1050 dominator would be better suited for the 427.

Are you sure it's lean?
Too hot a plug will burn white even if it's stinky rich.

I don't think your losing much on the carb-- sure you could get a glory # with a dominator, but the streetability goes down accordingly. I was suprised that a well prepped 750 (I have a VDL prepped one from my 358) dyno'd only 12hp shy of my 950cfm on a simlar build (see my garage link below), and both drew the same actual cfm through the air horn (880) on the dyno. I'd look at fuel supply (maybe line size), and if that ok, try another carb or tune the air bleeds.

You need to test with a gauge to see where the fuel pressure is at the big end, under WOT.
But, how do you mean it showed lean, what did the plugs look like? were they peppered or just real white? Plus, to properly read a plug, you need to shut it down after the pass, and then pull a plug. If it gets driven back to the pits plug reading becomes more and more inaccurate.

I say your carb is limiting i have a 383 and thats what i need to be running is the 850. I would say 1000 easily thats why you have to run such large jets. Your times shoudl easily be in the tens.