AFR meter or Gunson ??

Mysterytrain · 09-08-2004, 11:45 AM

Hey all, figured I would toss this out. I'm looking for a device to measure the CO on my 78 SC. I don't have an O2 sensor so what I have is a basic CIS system. New 3.2 short stroke rebuild with nice new SSI's that I'm not willing to weld a bung to! I love the accuracy of the AFR that Wayne is selling but I think it might be over kill for me. The Gunson is +/- .5% and that seems a bit coarse. Any thoughts on which one to spring for?

Paulporsche · 09-08-2004, 12:23 PM

Do you need an exact number for emission tests? I can't tell where you are.

Another option is to have a mech w/ an analyzer set it for you (not expensive) and go from there. JW recommends 3.5%CO. There are lots of threads on settings.

Mysterytrain · 09-08-2004, 01:07 PM

I'm in NJ. No, it doesn't need to be super accurate for emissions..I'm exempt from that. Just a shop tool I guess. Not sure if the AFR meter is over kill for me [although I'm really getting into being a CIS expert} would hate to buy the gunson if it was more of a toy then a tool.

Paulporsche · 09-08-2004, 01:11 PM

I don't have one. There are other ways to determine what your mixture should be, as long as you don't need to know exactly what the number is.

Mysterytrain · 09-08-2004, 01:51 PM

Paul,
I've seen the thread on adjusting the CO by lifting the air sensor plate..how accurate is this method? I'm getting anal about my mixture because the last thing I want to do meltdown my big bucks rebuild.

Paulporsche · 09-08-2004, 02:40 PM

I have never done this, but some on the board have said that if you raise the plate and the revs rise then you can go richer. If you lower the plate and the revs rise then you can go leaner. If you raise and if you lower the plate and each time the revs drop, then you are done like Goldilocks.

Since I have owned my car for 15 yr I can tell when it is too rich or lean by things like engine note, tailpipe color, popping and how easily it revs.

Since this engine is effectively new to you, why not take it to a reputable shop and have it set per JW's 3.5% spec to be sure it is in the right ballpark. You can just leave it there knowing it is probably quite close.

If you're like me (see motto below) then you can monitor and try these other things later, if you feel comfortable with them.

RarlyL8 · RarlyL8's Garage

I use both.
The Gunson gets you real close to where you need to be AT IDLE. The AFR meter lets you know what is happening in the entire RPM range.

cab83_750 · 09-08-2004, 08:21 PM

I'll buy Wayne's LM if someone will buy my Gunson for about 70% of the price...............Bueller, Bueller, anyone, anyone..

bkdamkr · 10-06-2004, 08:11 PM

I'll probably buy your Gunson. WHich one is is and what's the bottom line?
Thanks,
Brian

RoninLB · 10-06-2004, 11:04 PM

I measured my gunson against a shop 3 gas machine.. same reading.

Rondinone · 10-07-2004, 09:07 AM

This week I bought a single wire Bosch o2 sensor from advance for ~$18. The exhaust on a 911 is hot enough to heat it right at the tailpipe, so I shoved it in there and hooked a multimeter up to it. I've been fooling with my mixture based on drivability and sound, and the O2 sensor currently reads ~0.72V. I'll probably test it against my truck this weekend.

You need a good quality low impedence multimeter to read and O2 sensor. It won't tell you CO%, but it will give you an indication of lean or rich condition. If you're just interested in getting the mixture close to correct, this could be a cheap alternative.

RickM · RickM's Garage

You need to place the sensore before the Cat to get accurate readings....

kstylianos · 10-07-2004, 10:08 AM

Quote:

I have never done this, but some on the board have said that if you raise the plate and the revs rise then you can go richer. If you lower the plate and the revs rise then you can go leaner. If you raise and if you lower the plate and each time the revs drop, then you are done like Goldilocks.

Works like a charm......After you pass smog

From a previous post:

"I found that every CIS engine has its particular 'happy place' where it likes to run. No two are exactly the same but CO% usually falls between 2-3.5%.

This can be set by ear and its very acurate for best performance. If tuning CIS w/ lambda, disconnect the O2 sensor first.

The trick to find your engines happy CO is to get the engine at least running and with the airbox cover and filter off, SLIGHTLY lift the air sensor plate via the exposed elbow with a finger, knuckle or whatever. All is needed is very slight pressure to notice any change in RPM. If the engine RPM increases it wants to be richened. This is also true if you were to pull down on the sensor plate. If RPM's increase, then it wants to be leaned out. Make very small adjustments with the 3mm allen as necessary. The trick is to get the engine at a max RPM so when you either push or pull on the sensor plate, the RPM's will drop (from either being too lean or rich)."

Rondinone · 10-07-2004, 12:53 PM

Quote:

Originally posted by RickM
You need to place the sensore before the Cat to get accurate readings....

Only if you have a cat...

VaSteve · 10-10-2004, 12:35 PM

I used Charlie's method and it worked well. I fine tuned with the Gunson I borrowed. The metal hose that comes with the Gunson would not fit inside the Cat Bung. I went to Home Depot and bought some copper tubing for hooking up an ice maker (I'm not kidding - 1/4" outer diameter) and stuck that in the bung. Worked like a charm.

RoninLB · 10-10-2004, 01:23 PM

Quote:

Originally posted by VaSteve

fine tuned with the Gunson I borrowed.

I went to Home Depot and bought some copper tubing for hooking up an ice maker (I'm not kidding - 1/4" outer diameter) and stuck that in the bung. Worked like a charm.

which makes me think I could test carbs in 4th & 5th gear. I'd have a tube running into the cabin. I'd hold the rpms steady and that should give ballpark readings.. then I'll do a rolling dyno. cool