383 SBC Holley 750 eye burning stinky idle

[HQM383]

...on your list should be ‘fit an AFR gauge’.

I live and die tuning with my AFR gauge. I couldn't imagine a workaround otherwise (despite having had to do just that before they were available to the common man). I also have a vacuum gauge mounted in the dash.
It's not the tool for idle tuning necessarily although once the idle is confirmed best with a vacuum gauge and tach, I've found the air/fuel value can at least be referenced but it was very unlikely to be stoichiometric. With my cam (71°overlap), compression (10.2:1) and timing (30°at idle), AFR's were in or around 13-13.5:1.
Dialing in the cruise or WOT miuxture, while still tedious, at least gives a solid footing to work on.

Same here. They do have their inherent flaws like not being reliable at idle with performance cams. I do as you do and use the vac gauge to set idle and then refer to what the AFR gauge is reading. Almost always mine is around .92 - .94 lambda or 13.2 - 13.5:1 AFR (pump fuel I use is 14.4:1 stoichiometric) and I must have tuned 20 different carbs on my engine in the past 12 months. Still information to be gleaned from the spark plug but the real time feedback of a wide band is hard to beat for the non professional tuning carbs. Just a few days ago I swapped out boosters on one of my carbs. Touched nothing else and the AFR difference through the operating range was apparent. Dropped about .05 lambda on average when the mains would have been in play. The last km or so on the test route I drive is slow enough it doesn’t have the mains contributing so the plugs would have looked extremely similar before and after. Using the AFR gauge I know dropping a few jet sizes will be beneficial.

[rgalajda]

...on your list should be ‘fit an AFR gauge’.

I live and die tuning with my AFR gauge. I couldn't imagine a workaround otherwise (despite having had to do just that before they were available to the common man). I also have a vacuum gauge mounted in the dash.
It's not the tool for idle tuning necessarily although once the idle is confirmed best with a vacuum gauge and tach, I've found the air/fuel value can at least be referenced but it was very unlikely to be stoichiometric. With my cam (71°overlap), compression (10.2:1) and timing (30°at idle), AFR's were in or around 13-13.5:1.
Dialing in the cruise or WOT miuxture, while still tedious, at least gives a solid footing to work on.

Same here. They do have their inherent flaws like not being reliable at idle with performance cams. I do as you do and use the vac gauge to set idle and then refer to what the AFR gauge is reading. Almost always mine is around .92 - .94 lambda or 13.2 - 13.5:1 AFR (pump fuel I use is 14.4:1 stoichiometric) and I must have tuned 20 different carbs on my engine in the past 12 months. Still information to be gleaned from the spark plug but the real time feedback of a wide band is hard to beat for the non professional tuning carbs. Just a few days ago I swapped out boosters on one of my carbs. Touched nothing else and the AFR difference through the operating range was apparent. Dropped about .05 lambda on average when the mains would have been in play. The last km or so on the test route I drive is slow enough it doesn’t have the mains contributing so the plugs would have looked extremely similar before and after. Using the AFR gauge I know dropping a few jet sizes will be beneficial.

Farmers used to glean the field to collect leftovers after harvesting the crop

[PRNDL]

just to give you a different point of view. When messing with a carb many times more than one modification can fix the same issue. If I was to mess with it, first make the transfer slot is covered. If it needs more air to idle open the secondaries slightly, I personally don't drill throttle plate unless a last resort. Second I would play with the idle air bleeds. Go a little smaller first. If you are opening the throttle blades enough that fuel is dribbling out of the venturi, then a richer idle circuit may fix the issue. If that does not work try going bigger to lean the idle circuit. And always make sure the ignition timing is right before messing with the carb. If it has vacuum advance swap the hose from manifold vacuum to ported vacuum see what it likes better.

I agree with your method. I will keep the new plates in mind if all this don’t work. This carburator hates to have the secondaries open at all. I’ll get a stumble. Worse of a stumble than running on too much primary T-slot. I found a happy place here fronts A 3rd ratio. Front mixture screws sensitive as heck. Rear mixture screws as sensitive as I can get them but do not stall engine if I close them. It’s the best I can do. No more gray smoke, no eyes burning, still a little smelly but I think it’s normal.

Need to fix radiator
Change the oil
Change the plugs
And tune based on all the advice given above.
So far leaning the mixture to 1 turn on all 4 helped. Slowly tried 3/4, but as I went around the engine wanted to die.

Have you tried 1/2 turn each end with same amount of throttle blade open each end?

After ‘change the plugs’ on your list should be ‘fit an AFR gauge’. You may have the idle improved but that doesn’t mean the IFR and IAB are putting out a good AFR for cruise. An IFR of .035” is big for what you have. IFR is #1 to get right.

https://www.summitracing.com/parts/avm-30-4110

I have not tried 1/2 on each end with them the same. I will try that next. I have a feeling it may make the secondary mixtures more sensitive.

Man, you are right! AFR. I need to do that. Plus AED is sending me an assortment of IFR’s and IAB’s

Need to fix radiator
Change the oil
Change the plugs
AFR

[PRNDL]

So a small update. I discovered the sweet spot in bringing all 4 mixture screws to high sensitivity. Where they all function the same and any one of them will stall the engine if closed. It’s all centered around the primary curb idle being open 3/4 turns. No more and no less! Any more and the rears go dead and more than that and they all go dead.

So that settles where the primary idle should be.

In order to increase the idle, I had to open the secondary curb idle to 1/2. This carb does not seem to like that. No stumble but the revs are not crisp. More lazy. In order to fix that, I bumped my initial timing. I was able to get the idle where I want and secondary curb to 1/4 turn. Nice and crisp. But….


Two issues:
1. The engine is the happiest and crisp with the passenger side idle mixture screws at 1 turn and driver side at 1-1/4. I tried to balance them and the vacuumed would fall. I was able to get the vacuum to 12hg in park. Should I try this in Drive?

2. This engine takes all the initial timing I give it. It just gets smoother and smoother. It likes the initial in the 40’s. Idle way better now in the 30’s. Rpm’s and vacuum just kept climbing as I increased.

The distributor is electronic and I can set idle to whatever I want separate from the timing curve. I have it idling at 36 for now. 40 seems to be the sweet spot. Any thoughts?

TDC was confirmed 10 times or more.
Electronic ignition accuracy confirmed with 2 timing lights. No. Dial back.

[rgalajda]

The front idle mixture screws are more sensitive because of the drilled throttle blades.

When setting up a carb for best idle, initial timing is everything according to cam specs you are running. You said you have 42 degrees advance at idle.

On a 4 corner idle carb if the idle mixture screws are more than 3/4 turn range out for best idle , then the IFR is too small.
If the idle mixture screws are less than 3/4 turn range out for best idle , then the IFR is too large.
For example 1 turn out on all 4 screws is an acceptable range.

The IAB can be used to fine tune this ( simply because it is easier ) by a few thousands.
I prefer to start with the IFR.

To begin idle mixture screw adjustment you can start at 1 turn out ( for 4 corner idle ) and slowly adjust 1/4 turn in on each screw, then readjust idle speed ( probably 750 rpm for your cam ) in gear for automatics, fully warmed engine .

The IAB and the IFR have a relationship size wise.
You have a .075” IAB with a .035” IFR
Some Holley carbs in 750 cfm range have .070 IAB with .033 IFR

When drilling primary throttle blades, to obtain an acceptable idle , usually you would start with a 1/16 hole and test before going larger.

All of this means nothing if you have a vacuum leak somewhere.

[Schurkey]

I think you are right about the misfire.

Stinky, eye-burning exhaust at idle is usually more a matter of misfire than fuel mixture. Lean misfire stinks and burns your eyes, rich misfire stinks and burns your eyes. Perfectly-tuned carb, with a misfire from some other problem, stinks and burns your eyes.

A somewhat-rich mixture drives the CO high, but CO is colorless and odorless. Doesn't burn your eyes. As the mixture goes even richer, HC climbs...but not near as much as a misfiring cylinder. It's the HC that stinks and burns your eyes.

Fixing the misfire will make carb tuning easier.

[PRNDL]

The front idle mixture screws are more sensitive because of the drilled throttle blades.

When setting up a carb for best idle, initial timing is everything according to cam specs you are running. You said you have 42 degrees advance at idle.

On a 4 corner idle carb if the idle mixture screws are more than 3/4 turn range out for best idle , then the IFR is too small.
If the idle mixture screws are less than 3/4 turn range out for best idle , then the IFR is too large.
For example 1 turn out on all 4 screws is an acceptable range.

The IAB can be used to fine tune this ( simply because it is easier ) by a few thousands.
I prefer to start with the IFR.

To begin idle mixture screw adjustment you can start at 1 turn out ( for 4 corner idle ) and slowly adjust 1/4 turn in on each screw, then readjust idle speed ( probably 750 rpm for your cam ) in gear for automatics, fully warmed engine .

The IAB and the IFR have a relationship size wise.
You have a .075” IAB with a .035” IFR
Some Holley carbs in 750 cfm range have .070 IAB with .033 IFR

When drilling primary throttle blades, to obtain an acceptable idle , usually you would start with a 1/16 hole and test before going larger.

All of this means nothing if you have a vacuum leak somewhere.

Ok good info regarding the drilled butterflies.

Yeah I had it at 42 just to idle. Anything in the 30’s and it wasn’t great. I reduced it because I worried 42 was too high. Now with the carb set better, I was able to lower the initial all the way down to 30 and it ran fine. Smoother and better with higher vacuum at 40 though.

Yeah, I know these IFR’s are too big. I I receive the AED care package they sent, it has an assortment. I’m going to try .033.

[PRNDL]

Misfire. Changing the plugs soon.


What are your thoughts on the “correct” initial timing? Does 40 degrees initial sound like a problem? The distributor has a normal sweep after that once out of idle.

[rgalajda]

idle advance 35 to 40 degrees is not uncommon for a cam like that, as long as it retards from that at off idle

[skinny z]

idle advance 35 to 40 degrees is not uncommon for a cam like that, as long as it retards from that at off idle

This is why I find using full manifold vacuum advance works so well for my collection of parts.
30-32 idle advance with half of that coming from the vacuum can. On easy acceleration (or otherwise), the vacuum drops and takes the timing with it.
Seeing as PRNDL has a programmable distributor, simulating that I doubt is a problem.
Speaking of which...

[skinny z]

. I’m using an electronic programmable distributor...

Which programmable distributor do you have?
This is on my "to get" list. Changing springs, vacuum cans, limiters, etc gets pretty old after a while.

[PRNDL]

It’s bad ass. It has start retard. Timing is on its own. They your total, all in, and has a MAP sensor. So you get cruise vacuum. I spoke to the owner of the company and he did not do vacuum at idle due to cars with big cams.
The distributor is stand alone. No computer box. You set it with your phone via blue tooth. You physically set the actual distributor to 10 degree BTDC with a timing light then lock it down. The rest is done from in the car. Plus you can see what’s going on from your phone while under the hood…..


Here are a few of my tables.

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8529AB2F-E7E4-4F15-9472-8410497AD3D2.png

[PRNDL]

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[PRNDL]

Progression ignition
It’s bad ass. It has start retard. Timing is on its own. They your total, all in, and has a MAP sensor. So you get cruise vacuum. I spoke to the owner of the company and he did not do vacuum at idle due to cars with big cams.
The distributor is stand alone. No computer box. You set it with your phone via blue tooth. You physically set the actual distributor to 10 degree BTDC with a timing light then lock it down. The rest is done from in the car. Plus you can see what’s going on from your phone while under the hood…..


Here are a few of my tables.

AD03DA9F-BE4D-4FA7-8B2A-1D987C211171.png8529AB2F-E7E4-4F15-9472-8410497AD3D2.png

[PRNDL]

It has vacuum in HG, KPA, timing, rpm, speed via gps, and even boost. It even uses your phones barometric pressure sensor to adjust. Those are screen shots from my phone.

816169B2-69F1-45BA-8EC4-D463ACEBF841.png