Will someone explain how to use an air/fuel gauge properly?

[XH29N0G]

I just installed an A/F gauge on my car.  I can read it at idle (it settles at 11.8 which seems quite rich but this is where the vacuum was highest for adjusting the carburetor 4 corner idle screws).  I can read it under acceleration in 1st and 2nd, but that goes by quickly.  It is in the range of 12.8 to 13.5 for my one acceleration test.  I can read it when cruising at 2500 RPM and it is somewhere around 13-13.5.  But when I set out to do these tests, it occurs to me that there are probably better ways, and most likely a set way - such as (strong or mild) accelerate with more of a load than given by 1st gear, cruise at x RPM, etc.... 

I am looking for any advice, I don't care how blunt. 

The engine is a 452 cu in (383 block) with 10.1:1 compression and a 5.19/5.11 cam ( 112 LSA and 236/246 duration) with edelbrock heads, a QF 830 ss and a performer RPM manifold.   

[justcruisin]

The A/F gauge is a great tool. INMO it is best to use data logging with other inputs. If like me you only have the gauge and no other sensors hooked up for data logging you can still record the readings while driving. I set up a vacuum gauge next to the A/F gauge and a camera in front to record things while I drive. The vacuum gauge is important as it shows you what load you have on the engine, a rev counter would be a good addition.
I tune in this order - idle, cruise then WOT. I also disconnect the secondaries and wire then closed to check A/F at WOT on the primaries to dial in the PVCR.

[Kern Dog]

I made a chart and had my wife ride along to record the numbers as I drove.
She is a great lady.

[flyinlow]

My A/F ratio gauge shows what  the left bank of my engine is getting about 0.2-0.5 seconds behind real time.  Slight delay due to the time from when the carb mixes it until it is pumped thru the engine , burned and then sampled in the header collector and displayed. I chose the analog (needle) display. My readings are about 13:1 idle (smoothest), about 15:1 at cruise, and about 12.5:1 at WOT.
!4.7:1 is the perfect ratio.  Leaner compresses air that won,t be used for combustion, wasting energy and fuel. Richer wastes fuel, makes your oil and plugs get dirty faster and of course makes more air pollution. Richer is desired for cold starts, initial throttle opening (accelerator Pump) and rich best power for Wide open throttle use. About 12.5 -13.0 :1
The gauge will show richer during deceleration. As much as 9:1 for short periods when the car is pushing the engine with a closed throttle.t will also show rich if your choke is not working correctly or the floats are incorrectly set. It can show fuel delivery problems. At WOT the A/F starts off correct and then 10 seconds later goes lean. Larger carb seats fixed that problem. The gauge has reminded me to turn off the choke. It told me the carb had starting running very rich at WOT before my buddy told me about the black smoke when I nailed it.
Sticking air valve.
Your numbers would appear to be in the ballpark. Idle and cruise are easy. WOT is best done with a laptop or observer. (Wife's are not normally good choices for observers)

[XH29N0G]

Thank you all. 

I did figure out how to log data with a laptop.  Let me ask for a clarification.  I have a few questions about these responses.

I believe WOT is full acceleration rather than steady high RPM.  This correct, right?

I don't have a rev counter and have thought about that.  I had not thought of a vacuum gauge for additional information.  Your responses prompted me to look for more information and I found information on the innovate web site and some other sites that walked me through and provided good information for me. (http://www.innovatemotorsports.com/resources/carb-central.php)  I should have figured this out before... 

[justcruisin]

Some good info there, yep WOT is wide open throttle. For what it is worth my set up is similar to yours and I use the QF830ss, it was way rich out of the box for my engine, it came with 78/86 from memory. It also comes with 0.037" idle feed restrictors which I found to big. I think I am running 0.034"s.

[XH29N0G]

A few experiments today.  I tested how the A/F on full acceleration (the WOT A/F) responded to changes in the accelerator pump CAM.  What I did was to roll at about 10 mph and the n mash the throttle while in second gear.

The carb was originally set up with a pink cam (#330) on the primary (which I read is supposed to deliver about 30 cc over the full range of throttle).   There is a brown cam (#336) on the secondary (which I read is supposed to deliver 37 cc over the 1st half of the throttle movement).  

I did tests with the pink cam (swapped the hole from 1 to 2 on the pink cam, the orange cam (#466), and the brown cam) for the primaries and left the original brown cam in the secondaries.  All tests with the pink cam look like the one below.  The orange cam is a little better, but still shows the same spikes to lean on hard acceleration.  The brown cam does not show a large spike and has a rich spot immediately on acceleration.  I wonder if it is too much (overkill).  

My interpretation of the traces are on the figure below.  My interpretation is that at high RPM the A/F converges on a value of about 12 (which may be a little rich), but I saw values up to 13 and maybe 13.5 on some tests so I am not inclined to change the jets.  

Are the interpretations on the figure reasonable?  Or am I missing something?  (This is my first shot at it).  

My impression is that the brown cam is the best, but it would probably be worth looking for something intermediate (a blue cam).  Is this reasonable (i.e., is it better to go rich to A/F of 11 instead of lean to A/F of 16-18 on hard acceleration.

Am I doing this wrong.  I am basically mashing the pedal from a rolling start in 2nd gear at about 10 mph.  If I use 1st I get the same type of trace, but it ends very fast (2-3 seconds) because I hit 6000 RPM in that time.

[justcruisin]

I think your comments are on track - however - I'm pretty sure the brown cam is a 50cc pump cam and not to be used on the 30cc pump, might pay to check. The QF830ss comes with a 30cc front pump and a 50cc rear. You may be damaging the pump if you are using the brown cam on the front pump. Just a suggestion, but seeming as you are logging your output why don't you hook up a 1 bar map sensor and log the output over the top of your A/F reading. When you lift your foot the A/F will go rich, I think your mark for the end of your run is off, the map sensor will show this for sure though. Good work on your approach to tuning.

[flyinlow]

The effects of the accelerator pump discharge seam to be over my car in about 1 second. After that the ratio is pretty stable during WOT accelation.

[XH29N0G]

Thank you both.  I am learning a lot. 

I will look into other sensors.  I think I have reached the limit of what I am able to interpret confidently without additional information. 

I think you are right that the pump on the QF is supposed to be a 30 cc one for the primary.  There is a strange statement in their literature that the brown cam can be used for the 30 or 50 cc accelerator pump, but as far as I can tell it clearly hits the limits of its movement with my present configuration and I think your point that this could cause problems is valid. 

My next try will be a blue cam and if that doesn't work, then I suppose I would change to a 50cc front pump and use the brown cam, but I wonder if there is a better way to address this.

[XH29N0G]

Still waiting on the blue cam. 

I continue to test and have another result.  This time, I learned to disconnect the secondaries (fewer variables) and tried an orange cam.  I adjusted the pump more carefully and see less of a rich pulse with the accelerator pump.  I still see the lean spike beforehand, which I think is the air coming through before the pump shot makes it.  I am contemplating increasing the shooter (nozzle) size.  Does this make sense.

I also see the run converging on a better final WOT A/F ratio.  I am assuming I get this right and then reconnect the secondaries and work from there. 

[firefighter3931]

The effects of the accelerator pump discharge seam to be over my car in about 1 second. After that the ratio is pretty stable during WOT accelation.

Exactly ! Pump shot and squirter size tune for quick application of the loud pedal....used primarily as an enrichment circuit because the carb's main circuit cannot supply fuel fast enough. Basicly the accelerator pump circuit covers a momentary lean spot.

Try holding the throttle steady at 3000/4000/5000 rpm and get an AFR reading. That will point you in the right direction on your main jets. 
 
If it's not bogging the accelerator pump circuit is working fine.



Ron

[XH29N0G]

Ron,  Thanks.  I don't sense a bog.  I will try the steady RPM test either today or tomorrow.

I also forgot to post the image I made for the previous post.  It is below.  The solid line is the average of three runs.  The light lines are this line +/- one standard deviation.

[XH29N0G]

An update.

I have managed to get cleaner WOT (acceleration) traces in third gear.  I did a test with primaries only and found that I could get rid of the initial lean spike (for the primaries only) by changing the nozzle to 040 from 033.  I also found that I could make the WOT A/F closer to 12-13 by making the jets one step lean.  (The primaries alone were rich 11-11.2 and with secondaries it was about 11.8.)

The trace below shows it with the one step lean.  

I have not been able to get the lean spike (bump) on initial acceleration to go away with the secondaries.  It actually seems to be about the same height and shape with different squirters.  I have tried from 025 to 040 and not noticed a significant change.  The ones in the plot are with a very small nozzle size (025).  I switched it back to 035 and notice no discernable difference.  

The cam on the secondaries is a brown cam with a hole at #1 that I assume was drilled when the motor was set up.  The slightly higher trace at a/f of 15 instead of 14 (aqua blue line is a blue cam 30cc).

I think this looks pretty good and am about to stop.  Does anyone have an idea about how to address the initial lean spike/rise?  I have not tried the yellow cam on the 50 cc pump.  Could it need even more gas on initial tip in?

[flyinlow]

Looks like it could use more pump discharge to fill in the  spike. However if it i running well with no hesitation or bog you could just leave it as is.   

[don duick]

does the sensor need regular cleaning? The dynos clean their sensors regulary as deposits on the sensor gives false readings.

[firefighter3931]

Looks like it could use more pump discharge to fill in the  spike. However if it i running well with no hesitation or bog you could just leave it as is.   

Sometimes you can drive yourself crazy trying to make things "perfect" 

A millisecond lean spot that doesn't affect performance isn't worrying about. 



Ron

[justcruisin]

You should calibrate them once every twelve months or so but I have never cleaned one, is that needed I mean - you don't pull the O2 out of your daily driver and give it a scrub. Maybe when you are testing multiple vehicles on multiple days it matters

[XH29N0G]

Sometimes you can drive yourself crazy trying to make things "perfect" 

A millisecond lean spot that doesn't affect performance isn't worrying about. 



Ron

This is still therapeutic for me.  I am going to keep trying for the time being.