No power

HI Thought I might get some help from you guys that know buicks inside and out. My NOS 1971 short block 455 which I just put a NOS 1970 cam in (1237665) and 1970 heads on has no power under load. I have new 750 edelbrock and sp1 intake, HEI distributor, Timing is at 13 degrees initial. It runs so well when sitting and throttle response is incredible. (This is a motor I just installed because the old one is tired. ) When I drive it there is no power intil I get the revs up. at 2000 rpm it will hardly pull itself up a hill. It stumbles until it downshifts and then it is a bit better. Has R44ts plugs. With foot to the floor it runs at about 60 or 70 percent of what it should have for power. The old 455 was running fine . What did I do wrong ? I just advanced the timing way up where I can't see the mark and it performs better on the road but I know it is still not right. The balancer hasn't slipped.

Several questions.

did you degree the cam when you installed it? May need to be advanced.
did you Chang the distributor advance? Set it up to be all in by 2500 rpm.
set total timing, with vacuum advance disconnected, to 32 degrees, don't worry about advance at idle.
is your throttle opening all the way?
brakes releasing all the way?

Didn't degree cam. I see now that i should have. Just changed the advance and It is running better and is all in at 2200. Throttle is opening all the way and brakes are fine. I installed another set of plugs and gapped them at 045 R44TS plugs and it is better now but not perfect. Just took it on a 7 hour run each way and got 22 mpg but it still has a stutter at 2200 now under load. Will change distributor cap again and new plug wires again tomorrow. thanks. i will let you know. Is .045 gap enough ?

You must be running on a half of one barrel on that Edelbrock to get 22MPG. No wonder it runs poorly it is not getting any gas! Ten or eleven MPG would be more appropriate.

The Eddy carb runs a "backward" fuel curve from the quadrajet and they get dangerously lean at cruise or WOT on a Buick 455. The Buick 455 came from factory with an 800cfm Quadrajet, so your carb choice also shrunk down the breathing ability. I like the SP1 intake, and use one on my convertible, and I have a modified Quadrajet I built on the top of it, flowing about 890cfm. You might loose some torque with that intake on a stock engine, but it really does well on my modified 455.

I could go back to a quadrajet as I have a couple of good ones.I will try one. What intake would you recommend ? My last 455 got 22m mpg (canadian gallon) as well with the same intake and carb. I have 3.50:1 gears and overdrive and it runs at 2150 rpm at 70 miles per hour . Have about a 29 inch tall tire. It is a 55 century convertible and weighs 4100 lbs.

I think your fuel mileage is good. Many of these big buicks can get good fuel economy when set up correct.
I would keep the SP1 on there, I like them, just stating that you might feel a little loss on the low side, but mine gained torque when added. The Buicks like that open plenum design and flow.

I like the quadrajets, of course, it's what I do at Quadrajetpower.com. Make sure you go to a Buick 800 cfm. If you want/need an electric choke, the 75-76 Buick 455 Quadrajets can be converted to electric choke.