Ok both of these readings are very lean. You are getting misfiring and that is causing the carbon on the plugs. Looks like your .040" wires are too big. Try smaller ones. A good idle target is around 12.8. A good cruise target is a little higher, around 13-14. You probably will not be able to get to 14.7 at cruise speed with a stock Holley, but it does give much better mpg. Over that is just too lean.
Both richer than where you are now.
The dieseling is most likely from hot carbon spots from it being too lean. Same with the bucking. All that should go away when you richen it up. When you were fouling the plugs in 30 miles before, with no wire, you were likely way rich. Use the LM-1 to wind up in the middle.

This is the first step: Before you touch the wires:
Adjust the mixture screws at 1-1/2 turns out, then re-adjust for best vacuum / idle increases.
Re-adjust idle. Repeat until you find the "sweet spot".
The sweet spot is when moving the idle screws either direction causes a 20-50 rpm drop. This is called a lean or rich roll-off.
Now if this idle adjustment sweet spot is NOT near 1-1/2 turns out, that is when you think about messing with the idle circuit.
A vacuum gauge and a temporary underhood tach are essential.
That alone may fix your basic problem.

You do not even need the LM-1 for this part, but it would be interesting to see what it says after you do the above.

 

Colourtune plug was basically a standard spark plug but with clear glass insulator. Idea being you could see the 'colour' of combustion at idle and set the mixture for best tune. Popular here in the UK in the 60's for those 'shade tree mechanics'

 

Hi MelWff,
Engine was a complete package and I also assumed the carb would be matched - not even close! I needed to change the plugs to a 5/8 style to allow removal with the Hedman headers installed. They are NGK BKR5ES which should be a good match to the original AC Delco 4. I could try going up in heat range. I don't think I'm chasing an ignition problem. But interestingly ... Leigh1322 suggests the lean condition could cause misfiring and result in sooty plugs.
I'll keep you all posted.

Joe

 

Hi Leigh1322,

When I'm back at the shop in a few days, I'll perform the adjustments you suggest and report back with results and LM-1 readings. I have a vacuum gauge and my dial-back timing light has a tach function.

Joe

 

You should consider an aftermarket metering block that you can tune your idle feed restrictions. You can also lower your float levels to reduce the fuel pressure in the idle circuit. The higher the bolw level the higher the head pressure so more fuel is pushed through the circuit. And as Lars mentioned your Idle air bleeds can be changed to a replaceable restrictor or add small air holes in your throttle plates to introduce more air just above the idle feed and transition slots. I pretty much changed every circuit to be tuneable on my tripower center carb and now its a very nice system with very spontaneous response where the old system was reactionary and slow


This has a great read on how the basic flow works and how things interact. If you are good at deduction you can see how one change will effect or systems.
https://www.motortrend.com/how-to/83...uretor-basics/

 

Also keep a log of all changes no matter how small and what the throttle response, AFR and general drivability is. Anything that is a hard reading and the initial feel is ideal to record. Going back to see what you have changed and not repeating something you already tried is key. IS your AFR gauge a wide band gauge?... IF you are above 16 you are too lean to be getting any good information adn mine wont read nearly as lean as yours.. I try to keep everything inall 3 phases inside the 12 to 16 range and no higher. 12-12.5 for the richest at wot and 13 to 13.5 for idle, 14 to 14.5 transition and cruising and 14.5 to 15 for a lean cruise on a climb before the power valve opens. Mine could see a bit better as I push 16 on a steep hill in a high gear if I dont get more into the throttle.

 

Hi Leigh1322

I've conducted these tests today. It seems to me that the idle adjustment makes very little difference. Perhaps my idle mixture is totally dominated by the 0.040 idle restriction I've introduced.
The last AFR tests were conducted with idle screws set to 2 3/4 out.

The main jets seem to come in around 2600 which I think is to be expected.


Joe

 

If your idle jets aren't affecting idle you may be into the transition circuit too far. You should have your throttle blades set to .020 -.040 exposure ofvthe transition slot. Then turn the mixture screws to adjust idle speed. If your AFR gauge reads too lean and your idle is to low then you need to add holes in the Throttle blades above the transition slot. This will provide a better signal on the slot

I don't have the hole size off the top of my head but you can easily find it. All the new carbs come with these holes.

 

OK good data!

At 2600 the main jet comes into play and you have a respectable 14:1 AFR. Not a problem there.

At every rpm below that you have very lean 16-22 AFR.
The idle mix screws give best vacuum at 2.75 turns out which is way too far, you should get best vacuum at 1.5 turns.
So the extra fuel from the idle mixture screws being way out is still not enough to richen up your mixture.
At 2000 you are running on the transfer slots and still way too lean.
You are way too lean.
Your idle/cruise circuit has the fuel so restricted that giving the engine more of that mixture, with the idle screw, does not help enough.
I suspect the .040" wire restrictors, since you mentioned you installed those, and you said it was so rich before it fouled plugs.
I think you want to be somewhere in the middle., between no wire restrictor, and .040".

Looks like you have a doubled up wire inserted into your idle fuel restrictor?
Try cutting that to 1 thickness of wire. Or find some thinner wire.
Then try the idle screw and AFR test again.

I like the spreadsheet. Keep track of your changes and you'll get there!

 

Hi Rescue Rogers,
Thanks for your help! I'm using the Innovate LM-1 wideband AFR meter. There are no holes in the throttle blades and I might need to go down that path if I have no success with reversing the IFR restriction I've introduced.
Hi Leigh1322,
Note there's a typo in the table ... vacuum at 2650 should read 21".
You are correct in that I've gone from a rich idle and transition to lean by introducing the 0.040 restrictors.
I left it at that because my fuel economy jumped from 7mpg to 15mpg (average over a few years). I'm now revisiting to improve the idle behavior and eliminate the low speed bucking.
I'll try to halve the restriction by going from a doubled up wire to single. I'll report back in a few days once I've had a chance to play with it again.

Joe

 

I would raise your idle to somewhere between 900 and 1100...it will help eliminate a lot of those idle issues

 

Hi Rescue Rogers,
I'll definitely raise the idle when this is sorted. You can see the AFR is still lean 16-17 at 2000 and I need to resolve that first.
The engine runs on badly after shut-off if I increase the idle now.

Joe

 

up your idle then reset your timing without the vacuum advance connected. Run on is a timing issue mixed with excessive heat in the cylinder from being lean igniting left over fuel fumes. If it persists, pull one your wires that are in your fuel block and start again. YO ushould invest in an aftermarket block or a new Holley one incase someone drilled that one to get more idle fuel. If yo uwan to tget deep into it you can drill it out, tap it and put your own bleeds in.....I did. And write down everything with time and date

 

Hi All,

A bit more testing today ...
Pulled the metering block to discover I had single 0.020 diameter wire in the IFR. Since the IFR is around 0.055 in diameter this results in a 13.2% restriction. Decided to halve the restriction down to around 7% using 0.014 diameter wire. Made the following measurements. It seems the idle screws strongly affect the transition and cruise mixture and seeing 13.5 AFR now at 2000 and up. Idle itself 700 and 1000 are still showing lean.

I don't want to go richer on transition and cruise and will need to do some street driving to see if the 13.6 at 2000+ causes any problems.

How can I make the idle richer without affecting the transition. I've left the setting at 2 turns out, 0.014 IFR restriction and 6.5 power valve.


Joe

 

The Idle circuit has air bleeds on top of the carb, fuel restrictors inside the metering block and emulsion jets in the metering block. You can control each of those in newer metering blocks. In old blocks you can drill and add restrictors or you drill the holes bigger or pull out the over size restrictor and press in smaller ones. As you just discovered the 3 circuits start off individually but are cumulative as youstep on the pedal. A rich idle mixture can make a richer transition and cruise. I did a lot of research through old articles, posts on older forums and watched carb videos to get into the weeds of Holley tuning. You can go to my 68 hotwheels thread and dig through until you find my carb tuning from the last couple of years. It's a tripower thread but it's all the same theory. Since you are lean at idle andvrich above that try raising your float level. It will push more fuel through the idle circuit

If you still have lean idle and rich above that you can open the restrictors and test, then close the air bleed and test. I think if you close down your throttle plate to get the .020 opening in the transition circuit it will cut your air down and give you more control in your circuits. It's a lot to explain and you really need to get into that metering block if you want to really tune a holley. These carbs can be tuned well once that light bulb comes on

 

I am glad the smaller IFR restriction worked.
Now it appears you need to balance the idle/cruise/transition circuit better. It's really all one circuit but yours is fatter at the top.
Rescue has a couple good suggestions.
For now fatten it up at the bottom and see where the cruise lands.
More float, less IFR, etc.
Then it might be time to look at the air bleeds.
You reset your idle screws to best vacuum again right?
How many turns out are they now where they give the best vacuum and roll-off?
There is really only one correct idle screw setting, I see you tried three.
Pick the one with the best vacuum, best rich & lean roll-off, and do a 20 rpm lean roll-ff if you like. That is the best setting.
Then tell us where that is, That gives us clues about the transition circuit mixture tuning.
Go for more idle rpm, mine always liked 850. With bigger cams, the extra overlap makes it go lean as you slow down the idle, because the reversion goes up as you slow down, and you are closing close down the idle transition slot.
There really is only one good transition slot opening on a Holley, around .020", square, and front & rear should be equal.
Different size transition slots front & rear cause all sorts of problems. So set the idle speed and idle screws as above, and the pull the carb and check the transition slots.
Keep in mind that opening changes if you change the idle.
How much are your two throttle plates opened?
Are they balanced?
Here is the best article I have found on tuning Holleys.
At least you only have to go thru all of this one time, you need to tune that Holley, and it's transtion circuit, to that engine.

 

Once I get that slot set I try to control the Idle as best I can with the mixture screws do I don't change the slot setting. It's a lot of adjust this, check your numbers, readjust that. Then check again
Adjusting one item will effect so many other settings

 

I just looked this over gain Joe, and your ignition timing seems pretty good. Those specs tell me you do have it on manifold advance, and have 15* from the vac can.

But I was wrong about the idle speed, it should not need 850, the stock cam is mild enough it should idle fine at 700. It does not have a lot of overlap.
(224/234 110LC)
But a lean mixture, like you have at idle/cruise, burns slowly and poorly, there is some misfiring going on, it is still burning as it goes past the exhaust valve, and out the pipes, so the exhaust valve runs hot, and the manifolds run hot, and that causes the dieseling by self-ignition from the hot exh valve. HC go up too b/c of the mis-firing, and late burning.
It might even like 4-5* more advance at idle. Some more advance at idle will help cool things off and settle it down. So will getting the AFR richer. The peak cylinder pressure spike needs to occur at 15 ATDC and both timing and AFR affect both how fast the flame front burns, and how many degrees of advance you need before that. Both will help. It is hard to say which one matters more at this point. But cranking up the timing by 5* for a quick test would be quick & easy. Just do not run it hard or let it ping, back off as soon as you hear any ping.

 

Hi Rescue and Leigh,
Firstly, thank you both for taking the time to think about my situation and suggest courses of action and explanations.
I have no doubt I'll get there but there is a lot of learning yet to come.

I will take the carb off and recheck the 0.020 slot and balance. A lot could have changed since I last looked at it in 2016!

Leigh, I did not go any further rich than 2 turns on the idle screws since that already took the transition to 13.6 and I was concerned about going back to poor economy and fouling plugs.
Consequently I did not establish the best vacuum and rich/lean roll offs ... probably should do that and record the results.

Rescue, I'll start again by setting transition slots and balance and begin measuring again from there. I'll recheck and raise float level if necessary.

I'll experiment with ignition timing, but with 26 degrees at idle, I would have thought it's ok and I don't want to mask the lean idle mixture issues.

Once again, sincerest thanks!

Joe

 

OK got it.
You now have a huge 10 pt change in AFR between idle and 2000 Rpm. 22 to 13.6.
That's enormous!
Super lean at idle and then richen up back to normal.
Reading the Burton tuning guide, they say the same as what I was thinking. You idle air bleeds are too small, and maxing out.
They need to be bigger.
But since you have such a drastic change, I suspect the air bleeds are plugged or partially plugged.

I would check that out thoroughly first.
With a small enough diameter wire you can probe them and see if anything unclogs.
Could one be different than the other? Are you getting the same AFRs on both sides?
Or only checking one side?

I had a plugged one once too.

Next thought would be a vacuum leak around the carb somewhere.

Or the front transition slot is almost closed at idle.

More clues, couple more things to check.

Keep digging, the issue will appear, eventually. They are not all that complicated. It's not a computer program with one bad line of code out of thousands! LOL

Idle screw at 2 turns out is not too bad, let's concentrate on the severe rpm skew for now.
Way too much air at idle, and it goes away as you open the throttle and get deeper into the transition slot. But it is the same idle/cruise/transition circuit?!?!

My guess is the slot is almost closed at idle.

But check the air bleeds too. The idle air bleeds are the ones on the outside, just inside the choke horn, directly above the idle mix screws.


Attached are the Holley 4150 Installation & Tuning Instructions. A little more basic that the Burton ones, and better pics.