Help with AFR tuning
#2912233
04/20/21 11:10 AM
04/20/21 11:10 AM
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Joined: Mar 2008
Posts: 562 Kentucky
clovis
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mopar
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OP
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Kentucky
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Got my AFR gauge in and was able to make a few passes. At some point I will try to do some data logging, but for now it is iphone video. It seems I am lean at idle and it moving to a lean condition up top, but I am unsure what exactly I need to be shooting for at each segment. I have read the high 12 low 13 is ideal for WOT but again just looking for input. This is one of best passes the car has made, but it is after I fixed my valve train issues so it may not be a good apple to apple comparison. The plugs look reasonable. These early season passes are the best air we get, 60 degrees and high 20's humidity. My first inclination is just fatten up the idle, then either move the main jets it up or fatten up the high speed air bleeds. Again, just looking for numbers I need to be aiming at. https://youtu.be/Gs1d44a-AvA
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Help with AFR tuning
[Re: clovis]
#2912235
04/20/21 11:15 AM
04/20/21 11:15 AM
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Joined: Jan 2003
Posts: 14,539 So. Burlington, Vt.
fast68plymouth
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The numbers you should be tuning for are on the time slip...... not the AFR gauge.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Help with AFR tuning
[Re: fast68plymouth]
#2912263
04/20/21 12:03 PM
04/20/21 12:03 PM
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Joined: Jan 2003
Posts: 8,082 Tulsa OK
Bad340fish
master
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master
Joined: Jan 2003
Posts: 8,082
Tulsa OK
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You will need to move it around a little to see what it likes. My car likes 13.0 and will slow down a little on either side of that.
I would be OK with lean at idle, with a big cam the overlap really messes with the air mixture readings at low RPM. My car is fuel injected and I can idle it as lean as 17:1 on the gauge but my target it set at 15.5 and it idles great like that.
68 Barracuda Formula S 340
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Re: Help with AFR tuning
[Re: clovis]
#2912562
04/20/21 07:55 PM
04/20/21 07:55 PM
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Joined: Jan 2003
Posts: 12,814 Benton, IL.
DaveRS23
Master of nothing...
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Master of nothing...
Joined: Jan 2003
Posts: 12,814
Benton, IL.
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Just tune the AFR for the best MPH. No O2 needed for that. But, the O2 is great for looking at the fuel curve during the pass. That takes a data log. With any cam at all, the O2 is worthless for setting the idle. As mentioned, the reversion compromises it's readings.
Master, again and still
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Re: Help with AFR tuning
[Re: clovis]
#2912643
04/20/21 09:49 PM
04/20/21 09:49 PM
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Joined: Jan 2003
Posts: 5,446 Indiana
YO7_A66
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master
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Indiana
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Since you know the idle is lean, I would suggest richen up the idle first then test because this will also richen up the rest of the readings up to WOT. Then if it is leaning out at WOT, then the HSAB are easy as they are an external change. If you don't have a selection of HSAB's, then open it up and change the secondary jets and retest.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Help with AFR tuning
[Re: YO7_A66]
#2912804
04/21/21 10:35 AM
04/21/21 10:35 AM
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Joined: Mar 2008
Posts: 562 Kentucky
clovis
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I do have a small length of exhaust on the car, maybe three to four feet that includes a free flowing sprint car style muffler (Knoxville) and an extension after the muffler. I run Hedman fenderwell headers so an exhaust is challenging to say the least.
I was worried about sealing everything up, as I do run a slip on collector. I was going to take them apart to seal them but in all honesty I wasn't able to get them apart as they have been together over 10 years. I was the hoping 10 years of rust had sealed up whatever leaks may have been there. I put the sensor about 9-10" down from the merge.
How do you know that you have a leak at idle versus a true lean condition?
I would have bet a steak dinner it would have been pig rich at idle but that is only because after about 5 minutes of run time in the shop my eyes are burning (yes the door is open). I had set the idle from vacuum reading and I do have the timing lock out, so it idles about 1500. I also had a situation last year where my plugs looked like they where new after a pass and no matter how much jet I threw at it, it wouldn't go any faster so I assumed it was a HSAB situation that was leaning it out on the very top end. While I do depend on MPH and 60ft., the reason I installed the AFR gauge was to eliminate some of the guess work when tuning as I am novice at best, but it is also why I come here.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Help with AFR tuning
[Re: fast68plymouth]
#2912878
04/21/21 12:49 PM
04/21/21 12:49 PM
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Joined: May 2004
Posts: 12,478 Taxes & Virus's R-US, NY
Dragula
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I Live Here
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Taxes & Virus's R-US, NY
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The numbers you should be tuning for are on the time slip...... not the AFR gauge. Ditto.....Fatten it up till MPH drops off, and then go back to highest mph jetting and take note of AFR...Or lean it out if its already fat until you hit the highest mph and lean it out till it falls off and then go back...Now Jetting is weather dependent so remember you may still be one or two off your best on any given day. I typically only tinker with the HSB once I get the jet where I want it. Much easier to do between rounds for weather tuning. Once you have done all that, where did the AFR end up? That is YOUR target. Now you need to dial in the transitions. I have also added one to my drag car this year and I have an updated Thumper to try out, so we will see. My guess on mine is 12.7-12.9 ish...It was on my street car before this one, so I kinda know what it liked.
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Re: Help with AFR tuning
[Re: MR_P_BODY]
#2913015
04/21/21 04:58 PM
04/21/21 04:58 PM
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Joined: Mar 2008
Posts: 562 Kentucky
clovis
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I am using a .120 needle and seat, so move to a .130?
So is the intent just to put more fuel in the bowl? If so, could fuel pressure or float height be moved? Remember I am trying to educate myself.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Help with AFR tuning
[Re: MR_P_BODY]
#2913108
04/21/21 07:16 PM
04/21/21 07:16 PM
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Joined: Mar 2008
Posts: 562 Kentucky
clovis
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I am running just a shade over 6 lbs of pressure. The fuel level is just below the mid point of the sight glass.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Help with AFR tuning
[Re: MR_P_BODY]
#2913184
04/21/21 09:59 PM
04/21/21 09:59 PM
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Joined: Mar 2008
Posts: 562 Kentucky
clovis
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Just for my education.
Is the needle/seat change for a possible aeration issue? I am trying to gain some understanding of when you know which variable to change. I have read a lot of Mark, Tuner, Dwayne and Thumper along with hanging out a little on SpeedTalk trying to take some of the theory and make a practical application, so I appreciate the help and patience.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Help with AFR tuning
[Re: clovis]
#2913389
04/22/21 12:29 PM
04/22/21 12:29 PM
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Joined: Mar 2007
Posts: 3,298 West Coast, USA
jbc426
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master
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West Coast, USA
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I am running just a shade over 6 lbs of pressure. The fuel level is just below the mid point of the sight glass. I tried using those screw in plastic sight "glass" float bowl plugs, and my float level was significantly too high when just below the middle of the "window". The ones I tried are only designed to be used to set the float level and then must be swapped out with the brass plugs. I ended up setting them so the fuel was just visible at the very bottom of the viewable plug, and that car liked that better. That is where I understand the float level should be. I also run my outboard carb's fuel level a touch higher than my center carb's fuel level, but the outboard carb's float level is still well below the half way point. Maybe I am setting them wrong? Do you have an actual glass float bowl plug?
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Help with AFR tuning
[Re: jbc426]
#2913672
04/22/21 10:09 PM
04/22/21 10:09 PM
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Joined: Mar 2008
Posts: 562 Kentucky
clovis
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I really don't know what size the carb is, as it is a bit of Frankenstein. It is basically an 850 Brawler with a Quick Fuel 950 annular main body and some older Holley 2 emulsion hole metering blocks. On the list it is C4. In my testing last year C3 seemed to work best with the RPM and 2" 4 hole spacer. but I hadn't run the 850 version with the RPM intake and 2" spacer, so that is what I used for my first test and tune. It's not pulling the front tires any more but the 60ft was better.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Help with AFR tuning
[Re: clovis]
#2913817
04/23/21 11:13 AM
04/23/21 11:13 AM
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Joined: Jul 2004
Posts: 19,318 State of confusion
Thumperdart
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State of confusion
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Guess I'm the odd ball who's not a fan of annulars in a crowded small venturi.....I have and always use down legs but as far as afr's go and like said, It's a "directional" tuning tool and the time slip and plugs have the final say.....
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Help with AFR tuning
[Re: Thumperdart]
#2914118
04/23/21 09:39 PM
04/23/21 09:39 PM
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Joined: Mar 2008
Posts: 562 Kentucky
clovis
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I'm pretty easy as I like whichever one makes it faster. I bought the annular just to test, as you indicated lots of folks have good things to say about them.
Last edited by clovis; 04/23/21 09:52 PM.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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