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Carburetor tuning with a wideband A/F guage. #1564803
01/18/14 12:21 AM
01/18/14 12:21 AM
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Granite Bay CA
Kern Dog Offline OP
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This weekend I want to dial in the Charger and get it tuned right. I recently had the heads ported and changed to thicker head gaskets to lower the compression. Previously it was near 11.0 to one with 190+ cranking compression and detonated on the pump premium 91 octane gas we have here in CA.
I have an AEM wideband EUGO air/fuel guage in the car with an O2 sensor in the RH header collector. Currently with the Grant 850 Demon carburetor I am able to get it to idle in the mid 14 ratio in neutral and in gear. Part throttle and full throttle are under 13.0 and even richer. I'm taking the wife along tomorrow to map the actual numbers while I drive the car. Its cheaper than dyno time.
This method of tuning is new to me. I've stumbled along in life tuning cars by how they feel rather than using any type of guage. Most of my experience has been with stock or mildly modified engines. This car raises the stakes and I want to get it right.
Is it fair to say that since I am able to get the A/F into range at idle, I should be able to get the part throttle and WOT into range with jets and power valves? Even though it reads that it is too rich, I smell no fuel and see no black smoke. I recall reading that for WOT the goal is in the 13.0 range but what is a good goal for part throttle?
After I get the carburetor dialed in, I want to work on the ignition. I have a Rev-n-nator ECU that I want to use. The instructions read that in most cases the timing needs to be retarded at least 2 degrees due to the unique manner in which the ECU works. This means that if I need more initial timing, I'll need to narrow the advance curve.
Last week when I drove the car I felt a bit of an off idle stumble and lower idle vacuum. I thought I read here that it is suggested to set the timing to the highest manifold vacuum. Am I remembering that right? Currently it is set to 19 degrees initial and 33 total without vacuum advance.
Any tips or suggestions?
Thanks, Greg.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564804
01/18/14 12:58 AM
01/18/14 12:58 AM
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IL, Aurora
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So I'm guessing it doesn't knock anymore? Wot usually is best around 12.5.... Remember to also read the plugs

Re: Carburetor tuning with a wideband A/F guage. [Re: ademon] #1564805
01/18/14 01:12 AM
01/18/14 01:12 AM
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Columbus Ohio
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Im in the same process. I always did the same, by the seat of my pants. I am using an 850 DP demon carb and it is showing the exact same readings. I can get it into the high 13s low 14s at idle but as soon as I am off Idle its in the low to mid 13s. WOT is still the same. Its 16 degrees here so I figure It will have to wait until spring to get it sorted out. I do know a slight misfire will show a rich reading. I am watching closely.

Re: Carburetor tuning with a wideband A/F guage. [Re: mopfried] #1564806
01/18/14 02:56 AM
01/18/14 02:56 AM
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Granite Bay CA
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I drove the car last week. There was no detonation at all. I'll admit that the weather was in the 50s but at 10.07 to one and a pretty big cam it should do fine.
Reading the plugs has been mentioned before but I'm not sure what to do. My understanding is that they have to be removed immediately after a WOT run. I have burned my hands trying this before with the tight clearance this car has. I was hoping that the Air/Fuel guage would be a good way to avoid burn scars!
I have a wide assortment of jets and power valves. Currently I believe I have #86 primaries and #94 secondaries. The original jetting was 85/93.
My plugs are new. The plug wires have about 100 miles on them. cap and rotor are fresh too. Misfire? I hope not since everything has been replaced.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564807
01/18/14 05:18 AM
01/18/14 05:18 AM
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Bend,OR USA
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I ran my duster 518 motor at or above 14.3 to 15.2 AFR at part throttle up here at 3500 Ft above sea level on my Innovate LM1 with the LC1 conversiion to dual wide band I did run a cooler plug than most, Autolites AR3911 and AR3910, I also ran both the Champion RC12YC and the RC9YC, the motor ran well with all of them I had it at between 12.8 to 13.5 AFR at WOT with the six pak and the single 1050 CFM Dominator carbs. I tested, I had issues early on with inadequate fuel supply(10 micron fuel filter between the tank and the pump )the motor would leave the line at 14.2 AFR and cross the finish line at Bakersfeild(in really bad weather conditions) at 15.8 I got lucky and didn't hurt it, don't try that yourself Tune it until you like it, lean it down until it feels bad, richen it up until it feels bad again, find the sweet spot you like Then look closley at the plugs for the part throttle driving and put in several new plugs when you go test the WOT runs IHTHs


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564808
01/18/14 11:37 AM
01/18/14 11:37 AM
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Indiana
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Tune the carb starting at the idle and then work your way up to WOT. If you jump around on your tuning sequence, it will take you allot longer to make progress.
At idle: if the engine makes best vacuum = best a/f for your engine. This may differ than one of ours.
Off Idle: Idle Air Bleeds/ Idle Feed Restricters will combine to give you the A/F that you are looking for. IAB's make tuning this rpm range a quicker process. Tune the off idle/low rpm cruising speeds to around 13 and see how it feels. Then lean it out to around 14 and see how it feels. Choose the a/f that is not lean enough to cause deination or heating up issues.
Accel to medium acceleration from cruising speed: main jets/power valve/power valve Restricters: tune these to keep your accel richer than your cruise but leaner than your WOT.
After the rest has been tuned, then use your rear jets/rear main air bleeds to tweak in your WOT a/f to around 12.5 for starters.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564809
01/18/14 02:32 PM
01/18/14 02:32 PM
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Benton, IL.
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In order to adjust the different circuits of a carb, you have to understand the different circuits AND how they overlap and transition to each other.

Do you have Emanuel's Holley book? Some sort of reference and instruction material is essential to get started. For instance, does your car cruise on the idle circuit or the main circuit? You need to know how to determine that so that you know which circuit to adjust.

I will say this; set the idle mix where the engine likes it best, not by a target ratio. I have one engine that likes 13.6 for idle and one that likes 14.1.

If you have 100% gasoline, the cruise will like about 14.7 which is stoich. But if you have 10% ethanol, that target will change.

My engine's preferred WOT ratio will usually be somewhere between 12.5 and 13.2 depending.

You'll also need jets, bleeds, power valves, small drill bits, maybe some wires and a lot of time to experiment. Trial and error is the path to success for you. We can give you some starting points or tell you what worked for us, but only you can find what is best for your particular combo.










Master, again and still
Re: Carburetor tuning with a wideband A/F guage. [Re: DaveRS23] #1564810
01/18/14 04:13 PM
01/18/14 04:13 PM
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Granite Bay CA
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Thanks for the suggestions so far!
I forgot to mention that here in CA the gas pumps have a sticker that reads "Up to 10% Ethanol" yet testing has found an average of 6% is common across the state.
It makes sense that each car may respond differently. The compression, intake port design, exhaust system, camshaft, carburetor and ignition of each car combine to be unique to any car screwed together 40 years after Ma Mopar had her hands on it!
I have a Holley book to peruse. I'll take a gander once I get out to the shop. Thanks again.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564811
01/18/14 04:31 PM
01/18/14 04:31 PM
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One of the toughest parts is figuring out which circuit you are on while cruising (let's say 30_70mph or so). As mentioned, once you know which circuit you are on, then you take allot of the guess work out of the tuning.
When you are out cruising, take notes of the a/f reading at different steady cruising speeds (ref: 30/40/50/60/70mph) then when you make a tuning change, write down the new a/f reading at these same speeds. This will show you exactly where your change made a difference good or bad.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Carburetor tuning with a wideband A/F guage. [Re: YO7_A66] #1564812
01/18/14 04:34 PM
01/18/14 04:34 PM
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Granite Bay CA
Kern Dog Offline OP
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Good idea. I'm going to take the wife along with a pen and notebook to record the A/F readings. I was planning on only doing a part throttle and WOT test but I'm sure that recording more info to digest could be helpful.

Re: Carburetor tuning with a wideband A/F guage. [Re: DaveRS23] #1564813
01/18/14 04:44 PM
01/18/14 04:44 PM
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Quote:


If you have 100% gasoline, the cruise will like about 14.7 which is stoich.




That is, without a doubt, the most incorrect and oft repeated myth ever.

The stochiometric ratio is nothing more than when exactly all oxygen is consumed and all fuel burned.

You can and should go leaner than that at cruise for mileage. You will be richer than that at WOT for safety. There is a very narrow band where stochiometric ratio matters and unless you are running cats it's irrelevant. You tune for what the engine wants, not some number someone who doesn't understand it's meaning tells you.


They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
Re: Carburetor tuning with a wideband A/F guage. [Re: Supercuda] #1564814
01/18/14 05:20 PM
01/18/14 05:20 PM
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Re: Carburetor tuning with a wideband A/F guage. [Re: Supercuda] #1564815
01/18/14 10:42 PM
01/18/14 10:42 PM
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14.7 is the one number the OP can target and be fine, not necessarily perfect, but fine. We can get into a lot more intricacies of this, but it would simply be over the OPs head. I readily admit that the 14.7 target is not likely optimum, but the OP doesn't really have the abilities to set the cruise any finer. The idle and WOT, he can.

Rather than limiting yourself to criticism, why don't you suggest the best process for a carb noob to set his cruise ratio. He has no tools, parts, or recording ability. At this point, anything more than I suggested will bury him.

I was only trying to help a noob get to an acceptable point, not give him an engineering lecture.



Master, again and still
Re: Carburetor tuning with a wideband A/F guage. [Re: DaveRS23] #1564816
01/19/14 12:01 AM
01/19/14 12:01 AM
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Granite Bay CA
Kern Dog Offline OP
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The wideband guage does have data logging capability but I haven't looked into that.
I think that if I can get it within the acceptable range, I'll probably be happy with that. I may be leaving some power or economy on the table since I am tuning without the use of a dyno or other sophisticated equipment.
The idle vacuum before the head gasket swap was close to 10 hg in neutral. Its now around 7 to 7.5. I advanced the timing to achieve the highest vacuum and while it moved closer to 10 again, the initial timing was then at 28 degrees! I can't imagine that it would be easy to start with it advanced that far.
I checked for vacuum leaks and found none.
I am grateful for any suggestions here but don't want to cause arguements!

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564817
01/19/14 01:28 AM
01/19/14 01:28 AM
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I agree it would be hard to start with that much intital timing. I have heard to back it up one inch of vaccum and check yout timing there. I use a Mallory box with a start retard. It drops as much as 10 deg for starting. I have also heard that you can kill the spark with a toggle switch and crank the motor and then add back the spark... I have never tried this myself..

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564818
01/19/14 01:33 AM
01/19/14 01:33 AM
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Bend,OR USA
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Figure out how to activate, download and read the data logging Mine would do that in real time or store a certain amount of time so I could down load it to my laptop later and look at it in the house or shop instead of trying to drive and watch the read out at the same time. Mine had the RPM packaged added when I bought it so that help also in looking at the results Watch the spark plugs closley after each modication


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Carburetor tuning with a wideband A/F guage. [Re: Cab_Burge] #1564819
01/19/14 03:30 AM
01/19/14 03:30 AM
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Granite Bay CA
Kern Dog Offline OP
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Reading the plugs is often mentioned.
I have never done this. I hate to sound like a newbie but in a 440 B body with 2" headers and power steering, how is this done without burning a persons hands? Every time I have changed the plugs I wait until the headers cool down. I'm a Carpenter by trade and obviously need my hands for work.
Isn't the procedure to run the car hard at WOT then shut down and pull the plugs immediately?

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564820
01/19/14 04:07 AM
01/19/14 04:07 AM
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Quote:

Reading the plugs is often mentioned.
I have never done this. I hate to sound like a newbie but in a 440 B body with 2" headers and power steering, how is this done without burning a persons hands? Every time I have changed the plugs I wait until the headers cool down. I'm a Carpenter by trade and obviously need my hands for work.
Isn't the procedure to run the car hard at WOT then shut down and pull the plugs immediately?




After your WOT run you can let the engine/headers cool before removing the plugs. The plug coloring will not change while the engine is off.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564821
01/19/14 04:23 AM
01/19/14 04:23 AM
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You are correct on the WOT tests, all the other tests on the idle circuit,, transition circuit, part throttle cruise can be looked at(the plugs) after letting it cool down Same thing on the WOT, let it cool down. DO NOT hurt youurself while tuning or driving This is suppose to be fun


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Carburetor tuning with a wideband A/F guage. [Re: Cab_Burge] #1564822
01/19/14 05:12 AM
01/19/14 05:12 AM
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Granite Bay CA
Kern Dog Offline OP
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Holy crap. I thought all along that the plugs had to be pulled on a hot engine because the coloring changed as the engine cooled down!
Okay, now that I've been "schooled" on that, what color am I supposed to be finding? Is a light tan color the goal?

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