Exhaust Analyzer Results

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73Swinger18

73Swinger18

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I took my Swinger w/318 to the carb shop to have them check the exhaust gases after a carb spacer change. The plugs look good and the car runs great. Not knowing much other than the basics of these numbers, does anything stand out to the trained eye? Two runs were taken at different RPMs as shown. Thank you.
IMG_20161220_162202.jpg
 
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Lelo Dart said:
No. Don't know what any of that means. I think all that is for emissions testing. IMO, what you want is the air/fuel ratio and before and after engine vacuum readings.
Item Detail Not Found | O'Reilly Auto Parts

Does it tell you anything? What did the the shop who did it say?
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They told me it looked good. It is running a tad richer then when I had the larger spacer installed, but the plugs look good and it runs well, so they said not to bother going down a jet size. Running rich will result in a higher CO reading. Running lean will result in a higher O2 reading. All I know is what I read from this www.crypton.co.za/Tto%20know/Emissions/exhaust%20emissions.html
 
7% CO sounds very rich at idle to me. The very low NOx also suggests over-rich with low peak combustion temps. As mentioned, a wide-band A/F ratio meter is probably a more useful adjustment tool in your garage.
 
71DodgeDemon340 said:
Cant you set air fuel mixture with a vacuum gauge?

Tuning carburetors and setting timing
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I set my mixture using a vacuum gauge. I just brought it back to the shop to compare readings they took when I had the open spacer installed since they weren't going to charge me anything. I really just wanted to see if it ran richer, which it did and see if anything looked unusual to you guys. Thanks for the replies.
 
73Swinger18 said:
I took my Swinger w/318 to the carb shop to have them check the exhaust gases after a carb spacer change. The plugs look good and the car runs great. Not knowing much other than the basics of these numbers, does anything stand out to the trained eye? Two runs were taken at different RPMs as shown. Thank you.
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To be honest, the numbers don't correspond to an Air fuel ratio if you look at a chart like the one that's in the article you linked to. Oxygen seems way high if there was no air pump. But there could be lots of reasons for that. Knowing that you put an open spacer under the carb makes me think this is hod rodded engine.

A really good tuner can take full advantage of a 4 or 5 gas analyzer, but it sounds like your people are a standard service station that is just using them for emmissions and troubleshooting stock vehicles.*

A spacer's effect on mixing and distribution will vary with speed and load. An open spacer is usually installed with the goal of improving wide open throttle in higher rpm (3000 up). Sometimes they can hurt distribution at low throttle and idle because of lost velocity. That's the only thing I'd be looking for on a steady state low rpm check like the two you posted. If you don't have a before and after, only a really smart cookie with lots of experience will be able to read much into it. However even if you don't, now you have a baseline.

The rpm of both runs looks to be at low throttle but above idle. On most carbs that's an area of the circuitry that's harder to adjust. It means fiddling with the idle air bleeds and sometimes the transition slot. Not that hard, but definately more than most mechanics get into.

*Examples:
Discussion of exhaust gas tuning tools.
A/F on a Dyno, Bruce "Shrinker" Robertson (archived post).
CO measurement, See also for Shrinker's comments on how CO readings are not directly accurate for useful for AFR.
Lambda [base reading WBO2 use for interpreting AFR] and emmissions.
 
Too much fuel at the 1100ish rpm, what jumps out at me is how low the CO2 is, WAY too low. Most relatively stock engines w/o a cat can easily put that at 11-12% in good
condition and tune. Some cat equipped ones have gone in the ^14's. Rich mix will jump the CO & the HC's up slowly, lean will drop the CO but raise the HC's quickly. The more
efficient you're burning, the more CO2, and the less O2 you will see. Basically, you need to start leaning the idle screws until the HC's stop dropping w/the CO, keep in mind
the idle speed needs to be kept after as you make the changes. The throttle plate position at idle will affect driveability, A/JformS just walked a member thru' the process for
checking this & working with it, I believe it started out as a "timing retarding" on a teener in the elec./ign. forum.
 
Killer6 said:
Too much fuel at the 1100ish rpm, what jumps out at me is how low the CO2 is, WAY too low. Most relatively stock engines w/o a cat can easily put that at 11-12% in good
condition and tune. Some cat equipped ones have gone in the ^14's. Rich mix will jump the CO & the HC's up slowly, lean will drop the CO but raise the HC's quickly. The more
efficient you're burning, the more CO2, and the less O2 you will see. Basically, you need to start leaning the idle screws until the HC's stop dropping w/the CO, keep in mind
the idle speed needs to be kept after as you make the changes. The throttle plate position at idle will affect driveability, A/JformS just walked a member thru' the process for
checking this & working with it, I believe it started out as a "timing retarding" on a teener in the elec./ign. forum.
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Thanks. I'm going to get some smaller jets ordered tonight. The plugs have a little more soot on the ring than before. I had it originally jetted with the taller open spacer. Looks like I need to lean it out a bit.
 
Well, main jets won't have a huge effect at 1100, but the idle mix screws are still well in play & have a big influence on the A/F at that RPM. Just the same, the 1900ish #'s are
a touch rich as well, so it certainly won't hurt to have leaner jets to give a whirl.
 
I would strongly recommend getting the idle right before messing with mains. Definitely go through the transfer-slot procedure first.
Also, that 1900 rpm is most likely in neutral (unloaded) so the mains are not likely to be flowing fuel. You could look directly at the boosters and see if they are...
 
DrCharles said:
I would strongly recommend getting the idle right before messing with mains. Definitely go through the transfer-slot procedure first.
Also, that 1900 rpm is most likely in neutral (unloaded) so the mains are not likely to be flowing fuel. You could look directly at the boosters and see if they are...
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Since this test at the shop, I did verify the slots and screwed in the mixture screws half a turn which yielded the highest vac/RPM.
 
Any updates on this, new analyzer readings etc.???
 
I added a PCV valve and pulled the carb to make sure the transfer slot was adjusted properly. Got it to run nice with the idle screw in a bit more (1.5 turns out). I'll have to bring it back when I get a chance and see what's changed. Plugs look good!
 
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