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Old 06-22-2020, 07:30 AM
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Had a very similar issue that smaller primary jets cured

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Old 06-22-2020, 08:28 AM
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Main Jets do not effect the idle air to fuel ratio in any way shape or form, but the idle air bleed jets outside the fuel bowl do!!

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Old 06-22-2020, 09:04 AM
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Is the carb new? If not, take it all down and clean all the main body, metering block and baseplate holes out. Mine was working fine on my old 455. Took it off for 6 mos. Had a red shop rag over it. Put it on the new motor. Running rich. Blew out the air bleeds. They had trash in the body.

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Old 06-22-2020, 09:10 AM
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Put the Idle Feed Restrictions back down in the lower position on the metering blocks.
I have fixed many many 950 HP carbs (as was said, not a true 950 cfm carb by any stretch).

They all run poorly until you fix the idle circuits properly. Lots of info in my Holley Carb Sticky.

Tom V.

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Old 06-23-2020, 10:48 AM
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Closed idle screws all the way and idle increased.

Removed carb, bowls, bleeders, idle screws (cork seals were disintegrating) power valve and primary and secondary jets. Flushed everything I could see with carb cleaner. Going to replace cork seals and gaskets. Secondary plates had holes that were epoxyed over. Should I leave those alone?
Lowered primary plates using idle adjuster to where I could see the top of the transition slot. I think too much transition slot was showing.

Wish me luck waiting for seals to be shipped.

Damian

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Old 06-23-2020, 10:56 AM
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I hope you were doing this with the carb turned over:

Quote: "Lowered primary plates using idle adjuster to where I could see the top of the transition slot."

With the carb turned over, (air cleaner stud pointing down), You should have a small square "window" above the throttle blade edge. The Transfer Slot is about .100" wide so the height would also be about .100" high.

Go by the width of the transfer slot, easy to gage the right distance that way without measuring.

Tom V.

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Old 06-23-2020, 11:04 AM
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"Secondary plates had holes that were epoxyed over. Should I leave those alone?"

Someone likely needed (or thought they did) additional idle bypass air at one time. Having epoxy on an area that could break off into the engine makes me a little nervous. Should be fine if the epoxy was applied on both sides of the hole, so less chance of peeling off the throttle blade.

Probably leave it alone for now, get the carb running well, then replace the blades or braze/solder the plates for a more secure fix.

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Old 06-23-2020, 12:18 PM
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Quote:
Originally Posted by Tom Vaught View Post
I hope you were doing this with the carb turned over:

Quote: "Lowered primary plates using idle adjuster to where I could see the top of the transition slot."

With the carb turned over, (air cleaner stud pointing down), You should have a small square "window" above the throttle blade edge. The Transfer Slot is about .100" wide so the height would also be about .100" high.

Go by the width of the transfer slot, easy to gage the right distance that way without measuring.

Tom V.
I believe I learned this "golden rule" from you Tom. Once I square my transition slot I never touch the front idle screw again. I use the rear blades for idle speed adjustment.

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Old 06-23-2020, 12:57 PM
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Glad I helped you out on that deal. BUT I learned that trick from Richard "Dick" Harroun,
who was the "on site" Holley Carb Technical Expert located at Ford's Dearborn Research Center. RIP Dick, you knew about 10,000 times as much about carbs as I ever will.

Tom V.

Google link for Dick's Dad (Ray Harroun) who won the very first Indy 500 Race.

https://en.wikipedia.org/wiki/Ray_Ha...dianapolis_500

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Old 06-23-2020, 05:02 PM
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Also there are two HP 950 configurations. The "classic" with 750 venturis and 850 throttle blades and another that is identical to a 850/1000HP in venturi and throttle blade size.

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Old 06-23-2020, 07:57 PM
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While I wait for the gaskets, is there a cleaning solution I can submerge the carb in to clean it?

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Old 06-23-2020, 09:48 PM
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Quote:
Originally Posted by Skip Fix View Post
Also there are two HP 950 configurations. The "classic" with 750 venturis and 850 throttle blades and another that is identical to a 850/1000HP in venturi and throttle blade size.
i remember when the biggest 4150 was an 850 and to get bigger you had to go to a dominator ...

i think somebody started rating their carbs differently and holley responded for marketing reasons? i thought i heard that somewhere. so the hp or street avenger carbs are rated differently than the old double pumpers, 1850, 3310 and so on?

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Old 06-23-2020, 10:44 PM
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Quote:
Originally Posted by Skip Fix View Post
Also there are two HP 950 configurations. The "classic" with 750 venturis and 850 throttle blades and another that is identical to a 850/1000HP in venturi and throttle blade size.
Just because I happen to have them on-hand:

- 750 and 750HP CFM
1.375" venturi x 1.688" butterfly

- 800 CFM
1.375/1.438" venturi x 1.688" butterfly

- 830 CFM
1.562" venturi x 1.688" butterfly

- 850 CFM
1.562" venturi x 1.750" butterfly

- 950HP CFM Classic 0-80496-1
1.375" venturi x 1.750" butterfly

- 950 CFM Street HP 0-82951
1.563" venturi x 1.750" butterfly

- 1000HP CFM
1.561" venturi x 1.750" butterfly

QF1000, has a 1.50 venturi x 1.750" butterfly

As for soaking, I know the old Berrymen Chem Dip (apparently before they changed the formula to be EPA friendly) was good for cleaning. Might still be. I use regular carburetor cleaner and compressed air.

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Old 06-23-2020, 11:15 PM
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Originally Posted by X72GPX View Post
Runs rich- burns your eyes blackens plugs.
When I hear about exhaust that stinks and burns eyes, my first thought is not "rich" but "engine misfire".

"Rich" mixture results in heaps and piles of carbon monoxide (CO). CO is deadly but it's odorless and colorless. Doesn't burn your eyes, doesn't stink. Silent killer.

Getting a stinky, eye-burning exhaust requires unburned hydrocarbons (HC). HC is merely "fuel" that didn't combine with oxygen. In other words, a cylinder's load of fuel/air went out the exhaust valve without burning.

A "rich" mixture has to be REALLY rich to go beyond excess CO to result in massive HC.

Quote:
Originally Posted by X72GPX View Post
I leaned all 4 corners, and idle is rough.
I would be looking for the misfire. Even a lean misfire will produce eye-burning "rich" exhaust.

Are the plugs black from excess fuel, or from excess oil? If fuel, is the mixture too rich all the time, or only at idle, or only at cruise, or only at heavy throttle?

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Old 06-24-2020, 08:21 AM
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Quote:
Originally Posted by surfsama View Post
Just because I happen to have them on-hand:

- 750 and 750HP CFM
1.375" venturi x 1.688" butterfly

- 800 CFM
1.375/1.438" venturi x 1.688" butterfly

- 830 CFM
1.562" venturi x 1.688" butterfly

- 850 CFM
1.562" venturi x 1.750" butterfly

- 950HP CFM Classic 0-80496-1
1.375" venturi x 1.750" butterfly

- 950 CFM Street HP 0-82951
1.563" venturi x 1.750" butterfly

- 1000HP CFM
1.561" venturi x 1.750" butterfly

QF1000, has a 1.50 venturi x 1.750" butterfly

As for soaking, I know the old Berrymen Chem Dip (apparently before they changed the formula to be EPA friendly) was good for cleaning. Might still be. I use regular carburetor cleaner and compressed air.
Good List there surfsama.

Comparing the first two carbs posted:
- 750 and 750HP CFM
1.375" venturi x 1.688" butterfly

- 800 CFM
1.375/1.438" venturi x 1.688" butterfly

Both carbs have exactly the same Primary Venturis & Throttle Plates with
the 800 cfm carb gaining 50 cfm with the slightly larger 1.438 secondary Venturis.

The next two carbs:

- 830 CFM
1.562" venturi x 1.688" butterfly

- 850 CFM
1.562" venturi x 1.750" butterfly

Both carbs have the same size Venturi 1.562" but Holley put the smaller Butterfly
Throttle Plate baseplate on the carb. By doing this they lost 20 cfm so now a 830 cfm carb.
So going back to the old 850 cfm throttle blade diameter baseplate you get the true 850 cfm airflow numbers.

Next two carbs (with Marketing Modifications).

- 950HP CFM Classic 0-80496-1
1.375" venturi x 1.750" butterfly

- 950 CFM Street HP 0-82951
1.563" venturi x 1.750" butterfly

We already saw that the 830 cfm carb was using the smaller throttle blades vs the 850 carb and lost 20 cfm.

So the supposed 950 cfm 80496 carb (actually a 770 cfm carb) had the same 750 cfm venturis and the better 850 cfm throttle base. So 750 plus 20 more cfm for the 850 sized baseplate or 770 cfm in reality.

The 950 cfm rated carb 0-82951 has exactly the same specs as the original 850 cfm carb but now they call it a 950 cfm carb. (100 cfm overrated for marketing purposes).

The only change being the choke tower removed vs the older 850 cfm double pumper 4781 carb. But they want you to believe that smoothing out the air horn area got you 100 extra cfm or the 950 cfm rating. Same logic applied to the 1000 cfm carb I guess except there the air horn removal got the 150 cfm extra flow. Sorry I do not believe that marketing hype in the least little bit. Do a test on a 1/4" radiused entry part on a flow bench with a carb and a test with a large bell-mouth entry, you will get the same flow. The radius is what makes the flow change not the bell-mouth expansion.

So that is my take on the carbs.

I haven't even mentioned the raised test pressure on the flow stand from the industry standard 20.4 inches of water test pressure to the inflated 28 inches of water

Always have to smile at that testing method. ADVERTISING HYPE

Tom V.

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Last edited by Tom Vaught; 06-24-2020 at 08:29 AM.
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Old 06-24-2020, 10:05 AM
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Would an issue with exhaust valves also be a factor, did the paper test on the tailpipe and it was flapping, like it was getting blown out and sucked back in. Think I might be removing heads over the summer.

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Old 06-24-2020, 11:34 AM
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Quote:
Originally Posted by X72GPX View Post
Would an issue with exhaust valves also be a factor, did the paper test on the tailpipe and it was flapping, like it was getting blown out and sucked back in. Think I might be removing heads over the summer.
slow down! you don't really know anything until you get the carb back on with the transfer slots square. if the engine dies with the idle screws all the way in, then you should be able to lean out the idle. if not, go to the next step.

a compression or leakdown test right now isn't necessarily a bad idea, but if you are a busy person just trying to get your car on the road and the car runs well otherwise, just focus on the idle circuit and forget everything else until that is figured out.

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Old 06-24-2020, 11:51 AM
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Good advice, Steve, thank you everyone!

Damian

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Old 06-24-2020, 01:04 PM
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Quote:
Originally Posted by Tom Vaught View Post
Good List there surfsama.

Comparing the first two carbs posted:
- 750 and 750HP CFM
1.375" venturi x 1.688" butterfly

- 800 CFM
1.375/1.438" venturi x 1.688" butterfly

Both carbs have exactly the same Primary Venturis & Throttle Plates with
the 800 cfm carb gaining 50 cfm with the slightly larger 1.438 secondary Venturis.

The next two carbs:

- 830 CFM
1.562" venturi x 1.688" butterfly

- 850 CFM
1.562" venturi x 1.750" butterfly

Both carbs have the same size Venturi 1.562" but Holley put the smaller Butterfly
Throttle Plate baseplate on the carb. By doing this they lost 20 cfm so now a 830 cfm carb.
So going back to the old 850 cfm throttle blade diameter baseplate you get the true 850 cfm airflow numbers.

Next two carbs (with Marketing Modifications).

- 950HP CFM Classic 0-80496-1
1.375" venturi x 1.750" butterfly

- 950 CFM Street HP 0-82951
1.563" venturi x 1.750" butterfly

We already saw that the 830 cfm carb was using the smaller throttle blades vs the 850 carb and lost 20 cfm.

So the supposed 950 cfm 80496 carb (actually a 770 cfm carb) had the same 750 cfm venturis and the better 850 cfm throttle base. So 750 plus 20 more cfm for the 850 sized baseplate or 770 cfm in reality.

The 950 cfm rated carb 0-82951 has exactly the same specs as the original 850 cfm carb but now they call it a 950 cfm carb. (100 cfm overrated for marketing purposes).

The only change being the choke tower removed vs the older 850 cfm double pumper 4781 carb. But they want you to believe that smoothing out the air horn area got you 100 extra cfm or the 950 cfm rating. Same logic applied to the 1000 cfm carb I guess except there the air horn removal got the 150 cfm extra flow. Sorry I do not believe that marketing hype in the least little bit. Do a test on a 1/4" radiused entry part on a flow bench with a carb and a test with a large bell-mouth entry, you will get the same flow. The radius is what makes the flow change not the bell-mouth expansion.

So that is my take on the carbs.

I haven't even mentioned the raised test pressure on the flow stand from the industry standard 20.4 inches of water test pressure to the inflated 28 inches of water

Always have to smile at that testing method. ADVERTISING HYPE

Tom V.
Whether high flow shafts were used, screws and the like will affect the flow to some degree.. I think that's why they are all over the place. We don't know specifics of those carbs listed.

I recently took the 950HP off dad's engine to replace with a 4150 Sniper Stealth. Here are some measurements I took.

The 950HP bore size right under the booster was 1.460"
The bottom of the bore was 1.710"
The blades are #325's which are 1.750" and come with air bypass holes pre drilled in all for blades, .093"
This carb has the high flow shafts and screws in the base plate.
And while the entrance of the bore at the booster seems small, this carb was able to support 724hp on a 571 ci Pontiac. I doubt it flows anywhere near 950 cfm.

The sniper stealth 4150 for interesting comparison is only rated at 870 cfm.
Yet it has no boosters in the flow path.
The bore also isn't tapered, as the top measures much larger than the 950HP at 1.768", more than .300" larger.
The bottom of the bore is around 1.685" and the blades are 172's which are 1 11/16"
While the blades on the Sniper are only .063" smaller than the 950HP, it has the added benefit of no boosters in the way, and much larger entry at the top (no need for venturi affect with EFI). Yet it's only rated at 870 cfm. Go figure.

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Old 06-24-2020, 02:41 PM
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If you design the Carb correctly the "High Signal" boosters remove a small amount of airflow vs a Open Bore Tube as the flow is determined by the throttle blades.

A Proper Entry to the booster section and a proper transition back to the throttle blades
caused very low flow losses.

Example provided below: Look at picture on the lower right of the patent.

EGR mixer for high-boost engine systems
Patent number: 8056340 is an example.

https://pdfpiw.uspto.gov/.piw?Docid=...iew+first+page

What I did was design a bore that had a slight venturi (like Holley did some of the 650 cfm 2 BBL carbs years ago)
and instead of pulling fuel thru the "venturi" it pulled EGR Gas thru the discharge holes under high boost conditions.

I know a little bit about how venturi and flow passages work.

Tom Vaught

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Last edited by Tom Vaught; 06-24-2020 at 02:47 PM.
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