383 SBC Holley 750 eye burning stinky idle

[PRNDL]

Good morning all.
I was hoping you guys help me? I’m at a loss. I have reached the limits of my little experience.

I have an AED Holley 750 HP body double pumper with 4 corner idle. Billet AED metering blocks and Holley base with the secondary transition slots higher than the primaries. 75 primary jets. 85 reads. 4.5 primary PV with a plug in the rear. .035 IFR and .075 IAB. Primary blades drilled 1/8. Pink cams in holes 1 and 31 squirters. Electric Aeromotive fuel pump and return style regulator set to 5.5 PSI, float bowls set at half way up sight glass, power valve not blown. No dribbling of boosters observed.

Idle stinks of raw fuel with a gray smoke, eyes burn, clothes smell, plugs blacken fast in carbon, my oil turns black fast, plus a lean stumble with backfire through the carb at tip i if I try to lean the idle. Wants a lot of initial. Idles best at 42 degrees at 900 rpm.

It’s on a freshly rebuilt 4 bolt 383 stroker .030 over and 6 inch rods. All forged and internal balanced internals. Zero deck 10cc D cup dished pistons. AFR 195 heads with 64cc chambers. 2.05 intake valves. 10.5:1 compression. Retro roller comp cams XR282HR 230/236@50 550 lift due to 1.6 roller rockers. 110 LSA. 106 centerline. Performer RPM air gap, 1 inch aluminum open spaces, headers, 2.5 inch exhaust, X pipe, and 20 inch dynomax turbo mufflers offset/center. Initial 30 min break in done, break in oil looked good when drained. Oil changed and only a few miles into the next 500 mile break in. Oil black already and a little low. Rings may not be seated yet.

3000 stall, th350, 3.73 gears, and 28 inch tires.

1972 nova on 93 pump gas.

Programmable ignition locked at 36 with 42 idle and low vacuum cruise at 46.

12 hg at idle in P or N and 8hg in drive

When I first installed the carburetor, I did it the traditional way. Secondary blades closed (cracked 1/8 of a turn to prevent binding), all 4 mixture screws at 1.5, and primaries set to 900 rpm. This meant 1-1/4 turns of the primary curb screw. Obviously too much transition and my primary idle screws were dead and secondary screws were hyper sensitive, stinky rich idle. Next I Tried phase two. Pulled the carb off, set the primaries t-slots to .020 at 1/2 turn of the curb idle screws and set the secondary throttle blades to match the fronts. Confirmed by holding the carb up to the light via light gap. No secondary transition showing (higher in the bores). Idle mixture screws back to 1.5 and started over. Primary screws came back to life but now the secondary idle mixture screws went dead. I could close them all the way and nothing. Plus developed an off idle stumble. It did not like the secondary idle open that far. Idle was at 900 rpm again with no change. Still rich stinky idle and black plugs. Next I tried a 2/3 method I read about somewhere. I left the primary setting at 3/4 curb idle .030 transition. Front mixture screws like that very much. I closed the secondary idke to 1/4 (1/3 of the primary) all 4 mixture screws came back to life, but idle was too low. 800 rpm. Idle still rich. I set the secondary idke mixture screws to only 1/2 and the primary mixture screws to 1.5 (2/3 ratio). It cleaned up the idle a lot, but a bad lean carb backfire developed. I returned all 4 idle mixtures to 1-3/4 and the stumble went away, but the idle stinks again. Seems I was able to fix the idle, but at a cost.

New Autolite 3924 turned black in only 3 days. New break Lucas 5-20 break in limit turned jet black in a few days. No smell of gas in oil and oil level did not raise.

Pink carb cams and 31 squirters. I stopped here and did not want to go down the rabbit hole any further and screw stuff up.

If I adjust to fix the rich idle, I get a lean stumble carb backfire. I was thinking of leaning the idle again with the secondary mixture screws at only 1/2 turn and tuning with only the primaries starting at 1.5 like I did above, BUT then fixing the lean backfire with an orange primary cam and 35 squirter. Backfire on primary throttle only. If I floor it and include the secondary pump, no carb backfire. I have not even thought about messing with IFR and IAB.

Lastly, I confirmed TDC like 10 times. Piston stop, compression stroke, both ways, marked the balancer, measured in the middle, both valves down, and so on…. All ignition components are new. Livewire wires. Not 180 off, wire / cap indexing and routing confirmed. Timing checked with two different non dial back lights. I’m using an electronic programmable distributor, MSD 6AL, and blaster 3 coil.

Any help cleaning up my idle and fixing my off idle stumble would be appreciated. Not to mention the stinky rich eye burning smell at idle, black plugs, and black oil.

Sorry so long. Any help would be appreciated.

[Baprace]

It's been my observation of carb smells that when rich it will smell like propane / rotten eggs and lean would irritate your eyes and stink. JMO

[PRNDL]

Good info. Interesting. The smell is like a gasoline vapor smell. Like someone spilled gas. I guess like propane. Plug gray smoke at idle, black plugs, and black oil. I was guessing raw fuel fouling plugs and getting in the oil. No AFR to confirm.

Do you know if F-bird still around?

[ClassAct]

That IFR is .005 bugger than I use to start. It doesn’t need all that fuel IMO. I’d start at .029 with a .070 IAB and tune from there.

[PRNDL]

Ok sounds good. I called AED about that and they are sending me an assortment of IFR and IAB. So try .029 IFR and .070. Will do. What about also switching from pink primary cam to Orange? And maybe from a 31 primary shooter to 35?

[ClassAct]

Ok sounds good. I called AED about that and they are sending me an assortment of IFR and IAB. So try .029 IFR and .070. Will do. What about also switching from pink primary cam to Orange? And maybe from a 31 primary shooter to 35?

One change at a time. Clean up the idle circuit first. And I forgot to mention if the IFR is up high in the metering block you need to move it down to the bottom. You can search this sight or the web and find pictures of where it should be if you aren’t sure.

[PRNDL]

They are high. AED metering blocks.

[bill jones]

---have you ever got your head out and over looking down into each of the 4 venturi areas with a good flashlight
---to watch fuel spray activities of the idle circuits
----and to monitor exactly rpm when the sprays start
---and get a good idea of what it looks like when throttles get up onto the transfer slots etc
---are there any small discharge holes above the T-slots?
---do you have any restrictions in the fuel path circuit to the T-slots yet?
------------------------
---and also watch for the exact rpm where the primary boosters start to flow fuel
---then changed the float level like 1/6th of the turn on the adjustment nut
---to where you can correlate float level with the booster fuel flow starting points
-----------------------
---if you take the float bowls off and turn them upside down---look straight in to float hinge screws
---where is the top of the float in relation to those screw head diameters?

---personally, I like the primary float screws to be fully showing
---which means the float level is down to where you can see'm
---and this height affects the rpm point where the fuel starts flow out of the primary boosters

[6.50camaro]

I pulled my hair out with the same issue on a Demon carb only to find the power valve gaskets hard has a rock and not sealing to the smooth billet metering blocks. Dan

[PRNDL]

I will try this Bill. Thank you

Sounds good Camaro. I didn’t check the PV gasket

[bill jones]

---speaking of power valve gaskets---I have occasionally found that the power valves once installed onto the meter blocks will bottom out on the inside power cavity casting
---might want to quickly check it without the meter block's outer gasket
---if it touchs the main body without a gasket use some bluing on the touched spots and then snug up the meter block with it's outer gasket
---and then pull it back off and see if there is imprints at the bind spots

---if that power valve touches the cavity at all it allows fuel to leak into that cavity area

[rgalajda]

Idle vacuum in gear ( 8 hg ) seems low for that camshaft. This may improve when you get things right. I would expect 10 to 12hg.
4 corner idle mixture screws should be around 3/4 turn out not 1.5 turns ( 1.5 turns is for a 2 corner idle carb )
Yes start the setup with the secondary throttle valves closed plus 1/8 turn.
Adjust idle mixture screws in gear ( warm engine ) for highest vacuum reading . All four mixture screws even.
Don't worry if transition slot exposure is up to .040" on primary.

Try this and report back. That backfire sounds more like an ignition problem. Lean idle should just be a hesitation/stumble.
You say primary throttle blades are drilled. I would be surprised if that cam would need that with 4 corner idle.
Was this carb new from AED? or a used one you picked up.

Also those jets are probably too large . You may end up as low as 70 pr and 80 sec.

[RevTheory]

You do have a pcv installed, right? Don't kick me, I've seen it happen, lol.

[PRNDL]

Yes sir. I’ll do this and report back.

The AED is brand new. It came with the blades drilled. They sold me this carb based on my engine. Seems so fat though.

Yes PCV hooked up and in use. Baffled high rise valve covers.

I think you are right about the misfire. It started started as soon as I installed these Autolite 3924 plugs. They blackened fast. Before that I had Accel shorties but they did not have enough reach. Ran good though. I’m getting NGK FR5’s installed in a few days.

My radiator blew so I’m having to fix that first.

[prairiehotrodder]

i would get NGK #5671A-7 spark plugs. Also listed as part number 4091

Brian