You fool, a 950 Holley is too big

I bought someone else's built 455 wrapped in a clapped out, cancer infested 69 Skylark. It has Edelbrock heads, 1.6 roller rockers, T/A SP1, hydraulic alleged T/A cam .505-517 lift unknown duration,etc., .040 hypereutectics, and a BG/Holley 950.
The carb is as it left the factory, 30cc pumps, 31 squirters, and a 6.5 power valve. It leans out bad around 2-2500 and I can't be the least bit aggressive with the throttle without a wicked stumble even shut down. Idle is rowdy at 1000rpm in neutral, 8" vacuum at idle in drive.
So I go to 2 local Chevy/Ford speed shops to get a 4.5 PV and possibly 35 squirters and their 2¢. Both said carb is Waaaaaaaaaay too big and I'm wasting my time and should put a 650 on it, maaaaybe a 750.

Thoughts??

 

LOL

 

cheby guys

 

Nice articles Larry

 

Put the 4.5 PV in. Better but still far from great.
BTW, jets are 77 primary and 83 secondary.

 

What's the timing......if it's only pulling 8" I bet it wants more timing down low.

Jets are way too low for my liking.....I would put 84/92. That's what I ran in a 950cfm 430 and 455 with sp1 and a very similar cam. When I tried leaning it down to 80/88 it wouldn't even run an 1/8 mile pass wot.

The bigger squirter will get more gas sooner, but shorten the pump shot duration. You need the pump shot to last long enough for the car to get pulling and running from the main metering........so you might need a bigger 50cc pump. And depending on what color cam you have a 50cc pump will require a new pump cam

 

A proper BBB carburetor uses a 750CFM as an accelerator pump...

 

17 base, 30 total by 3k. This GM hei is worn out as a retired cruiser NYC taxi, and probably is a major contributor. I just received Brent's MSD set up and haven't wrangled a set of wires for the install.

Also, got the MAP up to just over 10" by backing off the throttle screw and opening the center bypass. I should have checked the turns to get the transition slots square when I had the carb off. Right now it's 1/2 turn beyond contact, the rest is in the center bypass.

Pink cams, in the 1st hole

 

Depending on duration and overlap you might find locking the timing out helps the idle alot. I was able to get a 800 rpm idle this way.

But you jetting is way to small might not need as much as mine did, we ran a 4000 stall and 4.10 gears with no street time but your going to need more jet than 77/83. I would try a minimal of 5 or 6 jets higher on each side. I also prefer a little more spread, 8 jet size when running a pv.

 

I used 80/88 jets in my 400 small block to get the correct A/F ratio, and this was in an 850! I agree with Ben, I think you're way too small on the jets. On a side note, my PV was blocked on the secondary side so you might not need as much of a spread. Access to a chassis dyno would help but have you thought of one of those A/F gauges? I think you can get a good one for around $200.

 

I have considered adding AFR monitoring, I use one on the GN.
No rear PV on this carb.
Maybe next week I'll get the MSD in and some 88-90s. Also going to disconnect the secondaries to isolate the primary tuning.

 

Brett, your car being a 4 speed should have 3:42 gears. Only Stage 1 with automatic trans and no AC got 3:64 gears.

 

There are a couple different 950's out there now, but with your mention of the "center air bleed" I assume we are talking about an Ultra HP 950.. list number 80805xxx

Correct?

If so, this is a completely different animal from previous 950's, it's calibration is closer to an 1150 due to the size relationship of the throttle bore/venturi

But let's start by identifying for sure which carb you have, there were also E-85 and methanol versions of the new Ultra HP 950

JW

 

Didn't know the new hp were set up this way

 

I'll need to verify when I get home tonight. In October, I called the Holley tech to find out which carb it is. The previous owner claimed it was a Barry Grant 950. According to Holley that time it was a 950. Today they said it's an 820.

I know it has annular boosters, 1.75 throttle blades, no choke tower, Demon bowls, and a blow-back check ball in the PV passage. I can't recall the number on the air cleaner base flange, definitely does not have the traditional Holley list #