[X72GPX]

Runs rich- burns your eyes blackens plugs.
Current carb Holley HP 950 mechanical secondary
Specs- 462 cube, auto trans, heavy car.
Flat tappet cam
3.36 rear


Question-
Do you think it's over carbed and would I be better off with a 750 cfm vacuum secondary?

Thanks!

[PunchT37]

Nope. Carb needs to be tuned to your car.

[i82much]

might be better off with vac secondaries but you might be very happy just tuning what you have. should not be burning eyes or blackening plugs.

have you leaned out the idle mixture?

[leeklm]

Keep in mind that the 950hp only flows 830cfm, not 950.

Sent from my SM-G965U using Tapatalk

[X72GPX]

I leaned all 4 corners, and idle is rough.

[i82much]

does it stall if you turn the screws all the way in?

[X72GPX]

Yes stalls

[i82much]

does it have a huge cam?

[X72GPX]

240/244 @50

[i82much]

you should have no problems with your current carb. what is your ignition system? do you have access to a known good carb? float level correct?

[X72GPX]

MSD 6AL- Don't have access to a good known carb to try. Float levels are correct.

[i82much]

has this engine ever run properly with a different carb? new build? give us some history and details on the engine.

[X72GPX]

Before build it had a QJet and don't think it ran rich, built @10 yrs ago. Always ran rich since and seems to be getting worse. Any Holley experts near Northern NJ that you know of?

[ta man]

My. 950 HP is very sensitive to idle mixture. An 1/8th of a turn makes a difference. It took me a while to get mine to run clean. It does work well and actuall decent for mileage.

[i82much]

Originally Posted by X72GPX

Before build it had a QJet and don't think it ran rich, built @10 yrs ago. Always ran rich since and seems to be getting worse. Any Holley experts near Northern NJ that you know of?

sorry no. if i run into an issue i cannot solve, i would send my carb to forum member shaker455. i dont know him personally, just by reputation.

[Formulajones]

The HP 950 is a very versatile carb once dialed in for a particular combo. Many years back it was pretty common to use them on a wide range of engine sizes, from 350 on up. As stated they don't actually flow 950 cfm.

We've run 2 of them on a pair of cars here for decades. The Pontiac started out on a mild 455, then a pretty nice 463 and eventually found it's way onto a 571 ci Pontiac that supported 724hp with that little carb. In a car that weighs over 3900 lbs. All those engines only required some jetting changes, a couple tweaks on the idle circuit, and squirter changes when experimenting with intake manifolds. The other 950 I've had on my 454 BBC for 20 years and it's been a great carb.

I see no reason it wouldn't work on your combo. I'm guessing one or more circuits might need some attention but without having the car here it's almost impossible to say what or how much. Your elevation will play a big roll as well.

A safe place to be on jetting in that carb and that size engine that shouldn't be too rich, from my experience, if you're at least close to sea level, could be something around 76 in the front with a power valve, and probably 80 in the rear with a power valve or closer to 86 without a power valve. Give or take a number or so, that'll be in the ball park. If I remember right they come square jetted originally at 79/79 with PV's in front and rear, and I think the high speed air bleeds are 32 front and back.

This is assuming everything else is in good working order, blades set properly, idle circuits correct. Intakes and carb spacers will change things.

As a reference on the 463 Pontiac, with E heads and a 254 @ .050 roller, rpm air gap and spacer, 2" headers, it liked 80/86 jetting at sea level with both PV's where it ran the best. When on the 571, same heads and headers, Victor intake and super sucker spacer, it made best power at 84/92 jetting with the rear PV blocked. When at 5,000 ft elevation the front jets were dropped to 80 and a few idle circuit tweaks.

[tooski]

I had the same problem with a 750 dp (2 corner idle) on my 'little' 400. I messed a bit with the idle fuel and air bleeds. The biggest difference occurred was when I added 'idle bypass' air. AFR meter helped with tuning. Went from 11.3 to 13.8.

[i82much]

curious what your compression is, ignition timing as well.

[surfsama]

Do you have the correct power valve for your vacuum readings? Is the PV leaking? I once had a crack from a casting defect in a metering block so might want to take a close look.

I don't think it's the carb size. I run a 950 on my 433 with less cam and it burns clean.

[455-4+1]

Have run a 3310 750 vac sec deep into the 11's at 124mph on a similar engine in a heavy car. Great idle and throttle response, certainly wasn't holding it back any. Ran better than an 850 mighty demon with annular boosters, with better Street manors.
For anything down to 11 seconds on the street, it's all you need (and you get a choke ��)