Help with AFR tuning

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

The numbers you should be tuning for are on the time slip...... not the AFR gauge.

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.

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.

What kind of exhaust system is on the car? A wideband sensor only works at idle if the exhaust system is air tight. If there are any leaks then the recorded AFR isn't going to be accurate. Open headers are obviously very leaky as are race headers with slip tubes and old headers with warped flanges.

A good wideband will work okay at WOT with open headers but you really need a data logger to capture the information. The LCD screen won't be able to update fast enough to tell you much on a race car. The LCD type of gauges work okay for a street car with a tightly sealed exhaust system and a mild camshaft but they don't work very well with race cams and race exhaust systems.

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.

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.

The wideband sensor can't tell the difference between an exhaust leak and a lean condition. It just sniffs the amount of oxygen in the exhaust and reports back. It doesn't know where the oxygen came from since it is blind. You can't tell the difference between rich or lean with your nose since they both smell the same. A rich condition will burn your eyes and so will a lean condition. Best bet is to use the idle mixture screws to give you an indication of what the engine wants. Watch the vacuum gauge and the tach at the same time. You can also watch the wideband but don't necessarily believe the numbers, maybe just watch which way it moves.

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.

What needle and seat.. go up one size and try it again

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.

What is your pressure now... if the floats were way off it could cause you issues.. 120s should
be fine

I am running just a shade over 6 lbs of pressure. The fuel level is just below the mid point of the sight glass.

Everything looks fine... try the bigger N/S

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.

What size carb.....

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?

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.

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.....

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.

My 408 small block was tuned fastest with a 12.8afr and my 511 fastest is 13.2 or .3, but i do have slip tube headers and could be leaking a bit. 13.0 n/a on gas seems to be a good place to be in. Oxygenated fuel will change that.

I've rebuilt/modded em just not my first choice but some swear by them....