holley mixture distribution - Chevelle Tech
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post #1 of 13 (permalink) Old Dec 29th, 19, 12:17 PM Thread Starter
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holley mixture distribution

Any Holley gurus out there? the Performer RPM manifold has two plenums, one of which appears to be rich and the other is lean, #3,5,2 and 7 is supplied by the passenger side plenum and seems to be lean, I wouldnt expect this much variation between each side of the carburettor.
for comparison I dropped on an Edelbrock 1406 carb which was running on a 327 with no issues, although it was running lean at least all the plugs looked the same, all the soot was burnt off in 20 minutes, I want to put the holley back on but need to find out why it is out of whack first.
I have replaced the carb with a metal plate complete with barbed hose fitting, backed off all the intake valves and fitted a hand held vacuum pump, I applied 15" vacuum which took 1/2 hour to bleed off, I thought this was pretty good.
I suspect there may be a blockage somewhere, anyone had a similar problem or know where I should be looking? yes it pings under load and it is a 383 SBC 10:1 AFR 195 aluminium heads XR282 HR cam, Holley HP 750
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post #2 of 13 (permalink) Old Dec 29th, 19, 2:26 PM
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Re: holley mixture distribution

Looks like my plugs with the Air Gap I ran this past year. You can cross jet the carb, I believe it 2 jets richer on the RF and LR sides. GM used to put booster tabs on their Holley's to fix that problem along with the plenum floor directing fuel also. One thing I have noticed with a dual plane intake in particular is the old 300-36 Holley Street Dominator, it still has the same runners in the floor of the intake directing fuel. I know when I switched to the Dart single plane intake on my 461 all the plugs were perfect after the swap.
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post #3 of 13 (permalink) Old Dec 29th, 19, 5:18 PM
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Re: holley mixture distribution

I would take the holley all apart an run wire through all air bleeds and other holes and make sure no debris is in them.. blow out well and put back together and test.
Fix the pinging also.
Sounds like you would have a strong runner on your hands.
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post #4 of 13 (permalink) Old Dec 29th, 19, 5:34 PM
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Re: holley mixture distribution

Holley 750HP's are notorious for problems. I had one that did not work well and the jetting in them is too lean for power and their low speed circuits need to be re-calibrated. I switched to using Demon's as the Mighty Demons were better for me anyway than the Holley HP carbs. I have a 1000 Holley HP that has a huge hesitation no matter what I do to it, switch it over to the 1000 Mighty Demon car ran perfect. Being the plugs are black I would find the IFR and make it slightly smaller in the metering block to see what happens. Maybe that will take care of your problem, with what you have that engine should not ping with aluminum heads on 93 oct.
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post #5 of 13 (permalink) Old Dec 31st, 19, 10:08 AM Thread Starter
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Re: holley mixture distribution

I notice that one of my air bleeds is completely drilled through into the channel behind, as I have never messed with air bleeds I dont know what impact this would have but I guess it would mess up the balance between left and right. this is the side that was rich!??
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post #6 of 13 (permalink) Old Dec 31st, 19, 10:19 AM
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Re: holley mixture distribution

If you're talking about the holes that are drilled at an angle in the center of the picture they are called emulsion holes and all 4 should be drilled through into the main well behind them with a .026"-.028" drill.

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post #7 of 13 (permalink) Old Dec 31st, 19, 12:27 PM Thread Starter
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Re: holley mixture distribution

Quote:
Originally Posted by Tommy the Cat View Post
If you're talking about the holes that are drilled at an angle in the center of the picture they are called emulsion holes and all 4 should be drilled through into the main well behind them with a .026"-.028" drill.
Three of the emulsion holes are .026 into the channel behind, the fourth one in the photo is just over 1/16 ", I got this carb a few years ago but never used it before so have never seen it run properly, it starts and idles okay but the spark plugs are telling me something is out of whack when driving it.
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post #8 of 13 (permalink) Old Dec 31st, 19, 12:58 PM
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Re: holley mixture distribution

You've found your problem. Are you handy with a tap? It's not a big deal to fix if you have taps, drill bits and set screws.

I'd fix it for you but shipping might cost more than a new block.

70 Camino...Roller

69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt
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post #9 of 13 (permalink) Old Dec 31st, 19, 1:41 PM Thread Starter
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Re: holley mixture distribution

Quote:
Originally Posted by Tommy the Cat View Post
You've found your problem. Are you handy with a tap? It's not a big deal to fix if you have taps, drill bits and set screws.

I'd fix it for you but shipping might cost more than a new block.
this side was running richer than the other, (going by the plugs) I would think an oversized bleed would make it leaner?
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post #10 of 13 (permalink) Old Dec 31st, 19, 2:03 PM
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Re: holley mixture distribution

Those aren't bleeds. They are emulsion holes and a larger emulsion hole will cause a rich condition.

The air bleeds are external in the top of the venturi above the boosters.

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post #11 of 13 (permalink) Old Dec 31st, 19, 2:19 PM
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Re: holley mixture distribution

Perhaps Holley has the correct replacement block:

https://www.holley.com/products/fuel...ks_and_plates/

Or this might be the correct one:

https://allcarbs.com/product/holley-...etering-block/

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post #12 of 13 (permalink) Old Jan 1st, 20, 10:55 AM Thread Starter
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Well it isnt pretty but it is the right size now. The air bleed is only 26 which supplies air to the emulsion holes which are both 26
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post #13 of 13 (permalink) Old Jan 2nd, 20, 5:37 PM Thread Starter
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Put the metering block back on and went for a drive, it ran better but still pinged a little, I got home and while it was idling I checked the vacuum which was pulling 15 inches but I shut it down and pulled the plugs and still have #5, 8 and 2 different from the rest.
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