Hello MS ,  this is interesting !   https://www.youtube.com/watch?v=EY78uPXvvY0   
one day i will put an afr gauge !   imho  your data are perfect . 

So why do you think you need help tuning it Steve? Those numbers look like you've done a swell job. Those 68's look pretty spot on to me. I'm with BB on changing them. If you've got some extra time and enjoy bending over fenders, have at it. Me, I'd drive it as is.

Like the others said it's pretty darn good. Maybe try to lean the idle out a tad, I'd be interested in a 3rd gear WOT pull on level ground.

When tuning I always went for what the vehicle "wanted" rather than shoot for a specific number. Some would buck at part throttle when at a certain AFR and others were totally happy. Same thing with idle, some like it a little richer some like it leaner. So again just tune until you get the desired behavior. But again now that you have the wideband I'd look at WOT A/Fs.

HudginJ3 wrote:

In the interest of learning, where should the probe be installed with dual exhaust and and H pipe? I thinking right in the middle of the H to get the best reading that would be either too rich or too lean compared to the rest of the cylinders.???

Hi , no the h pipe is not the correct spot . It must be welded after the manifold exhaust , or with long tubes , just after the 4 into 1 . The sensor must work at high temp and crosspipe generally are away from hot . 

  top notch should be one on each side and two readings on the gauge . Have seen only one doin like that 

HudginJ3 wrote:

So do you have a switch on it to read each side individually or hook them together to get an average reading?

Generally reading a single bank is fine and is what most people do. If it varies widely between both banks there's something wrong.

The sensor needs to be as close to the merge point in the header as possible.  A single sensor in one bank is fine, especially for a carb application.  EFI applications use two if they have the ability to trim injector pulsewidth in each cylinder, though early batch fire systems used a single unheated sensor because they lacked this ability.  Even with the ability to trim individual cylinders having only two sensors still ends in guesswork, because what you really need is a probe in each cylinder.  High energy ignitions render plug reading impossible, so without that there's really no way to know what's going on in each cylinder.  Typically the factory uses a probe per cylinder when dyno testing an engine and sets the base calibration based off those results.  BUT, modern EFI systems are on engines that are typically so well designed that individual cylinder variances due to cylinder head, intake manifold, and exhaust manifold differences cylinder to cylinder are essentially insignificant.  So the tunability is there, but usually there's little to no trim in the base calibration from one cylinder to the next, though the system may use the trim function if it "senses" idle instability caused by a misfire, etc.

With a carb there's not much you could do cylinder to cylinder anyway, except maybe change plug heat range around a bit to try and cool or heat a cylinder that is lean or rich respectively.

And, as Hakan said, a 3rd gear pull on level ground at WOT is sort of the standard for power tuning.  BUT, without a time component the readings are somewhat academic, because it is all about what the engine wants.  Some of that you can do by feel, this will help you sort out a lean condition, but on the other side its hard to tell how rich to go without track testing for best ET.  Normally at the egnine's peak torque point I wold start at 12.5:1 and go from there, but that's also tricky because without dyno pulls how do you know exactly where that is?  Around here chassis dyno time is actually reasonable and there's a place that does a ton of it that's 20 minutes from my house.  Though, I do live in the most populous of the three counties in our nation's second smallest state   But, chassis dynos have popped up all over in the past decade, so with a little Googling you should be able to find one near you. 

There is not a level stretch of road within 20 miles of my house!  So, I guess my “tune it by ear” method must have worked ok.  It would be nice to lean out the idle, but it just doesn’t want to run if I lean it any.
It will be fun to see what mileage it gets on the bash trip.

Thanks for the input, guys.

If I recall, I am at about 12 BTDC

Maybe I missed this, but what A/F gauge are you running, is it permanent/temporay, and are you using a wide band O2 sensor?

MS wrote:

If I recall, I am at about 12 BTDC

Reason I ask is because I noticed when I installed an A/F gauge I tended to focus on fuel circuits at first, and your #'s are looking so good across the board I thought it may be worth playing with base timing just to watch the gauge and  observe its effect at idle.

I run up to 17* base even on stock motors and limit mechanical advance to 20*. It's tougher on the starter but always seems happier at idle for me.

It seems feasible to me anyhow that advancing the base timing, being such a simple check, might do the trick.

And I ofcourse agree with TKO and am not suggesting that is the fix, if it did clean up at idle you'd then have to do it right by adjusting the timing curve so as not to have too much total timing.

Last edited by Jon Richard (5/29/2019 10:52 AM)

MS wrote:

Thanks for the timing suggestion.  I am actually going to retard a bit, as I am getting some pinging on hard acceleration.   I have a custom Duraspark II curved for my engine by Davis.

Absolutely. I just think it's cool having an O2 sensor rather than reading plugs. Kinda makes me want to get other sensors and start data logging, just not sure I'm ready for all that.

Sounds like a nice ignition set up. You know I bought an old Allen syncrograph intending to restore it and do my own curving, but I've been bitten by the crank fired ignition bug.

I've been a member since the blue forum, I hope I can someday make it to a bash and put a face to these screen names!

I only use plug cuts when I doubt the O2 sensor which happens now and again because I have to run leaded fuel.  I replace sensor often. Plug cuts are a pain. I start with a brand new set of plugs run a couple of laps and cut power towards the end of the longest straight. Pop it in neutral and coast as far as I can hopefully to pit lane. The thing I have found is that richer is sometimes better than leaner since that whole combustion thing is so complicated. Based on looking at the torque curve, sometimes there seems to be a hole in it then it clears off and goes good. If that hole is in an important spot in the curve, I usually find that richer is better for lap times.