I agree with baddad457 completely. That's absolutey the wrong carb for that engine. It's like putting D batteries into your TV remote. I would take that thing off of there at once. You can try to crutch the big fuel leaker, but it's never going to run right.
Nevermind what other people run--they are usually lying, wrong, and most of the time, both.
Your 351, assuming it has stock heads, is probably good for 5,000rpm. It might spin faster, but it probably isn't doing much good past 5,000. Using the old RPM*CID over 1728 (cubic inches in a cubic foot) and dividing by 2 because it's a 4-stroke, and multiplying by .8 because your motor is optimistically 80% efficient at flowing air, you arrive at 400cfms. That would be the carb rating of a 4bbl, which is rated at 1.5" of mercury negative pressure in the intake manifold. You should be running a carb as close to 400cfms as you can.
As baddad said, you've got a weak signal, which means bad mixing and a confused intermediate circuit. When you pick a power valve, you have a vacuum gauge in the car and you drive it watching what the needle does when you accelerate. For instance, if you have a 6.5 powervalve in there, when the manifold vacuum drops to 6.5hg, the valve opens. If you are idling at 15hg and everytime you accelerate normally from a light your needle drops to 3hg, you need to get a 2.5 powervalve. Running a carb meant for a race motor on a stock motor means it's not going to work. That carb may work on a 351, but on a 351 that makes it's max torque at 5,500rpm and shifts at 7,000.
You need a carb designed to function in the rpm range you use. A drag motor that idles at 1,500, shakes the mirrors so badly you can't see out of them and leaks raw gas out of the headers isn't a performance engine in a truck that needs to make torque at 1,000-4,000rpm. The old 1850 Holley has much smaller primaries than your big double-pump and uses only the amount of secondaries that is can operate. It won't be very much--just a crack of them at full power.
Tuning a carb is tedious enough. Tuning the wrong carb is impossible. Throttle response will be weak, you might even get fireballs up through the throat when you try to romp on it.
My last hotrod was a 472" 1971 460 in a '64 Galaxie. It ran 13s on pump gas with iron exhaust manifolds, quiet mufflers and a 3.00 axle with a C6. I used a 600cfm AFB, and used ALL of it. It had razor sharp throttle response and pulled to 5,000rpm.
Do you want to go fast or brag about your parts? Get the right thing on there.
Welcome Visitor! Please take a few seconds and 
