I have to agree with this, maybe that clamp works on certain exhausts, but it sure didn't on my frankenmuffler.

Carbs are hugely sensitive to load and you won't get any accurate results measuring the CO near the exhaust tip, so what you have learned so far is less than you think. Not only will you not know anything about the mixture in normal driving conditions, I'd bet your idle mixture isn't as correct as you think it is. If you don't want to drive it on the road during winter, you can run it on a dyno, which is a much better place to tune it anyway.

JR

In terms of location of the sensor:

I recall the specs for Bosch 4.2 and later 4.9 sensors typically operate at 930C and 1030C for short duration.

Exhaust pressures do affect readings/ signal and Bosch has formula (for those enjoy their algebra) to estimate it. So locating a sensor can be critical. For the Carrera the sensor is located pre-cat. Depending upon the motor design and brand, today you find 2 sensors, one pre cat and one post cat.

If you looked toward a WB system, say AEM, they offer a mod kit to compensate for systems that have varying back pressure, such as with a turbo.

I'm playing around with 6 sensor system, one for each primary, and plan to run another on one of the banks to check avg after the collector. Don't have data yet so can't comment on the outcome.

In the past, using a single WB sensor at the typical 1 bank (1-3 cylinders) pre cat location, checking AFR's above idle, I prefer under load (driving). I have noted differences at any given rpm (driving vs sitting). That could be due to lots of things.

If you can get Sal Carceller to chime in his experience with AFR tuning would be quite helpful to you.

I have a Daytona-sensors WEGO IV. It has a single head unit with digital readout and up to 2 hours of data gathering. It records AFR, RPM, and MAP. i can see real time AFR and can download data to my laptop for analysis later. For around $400 you get a complete high quality system. Mine has been permanently installed for 8 years and has been great to tune my MFI. Pelican sells this unit. Highly recommended.

I have a Bursch exhaust. Bung is at the 2 into 1 before the main muffler.

I'm going to disagree. I've actually learned a lot and now have my car idling better than it's ever has. All systems need to be taken with its faults, although what I'm doing is not perfect and i wouldn't track the car it's 100 times better than doing it by feel.

Trust me, you need to measure the exhaust gas much further in than the tip. Pick up a book on 4 stroke intake and exhaust tuning and you can read all about why this is so.

My original reply had a typo. "Dump" was supposed to be 'Dyno." I started tuning carbs on a dyno in the late 80's. You'd be amazed at how sensitive carbs are to throttle position. Fuel flow occurs from a pressure differential and this differential is created by the velocity of the air through the venturis. You really can't duplicate what conditions the carbs see when driving down the road, without putting the engine under load. Dynos make that job so much easier.

JR

CIS Mod..........
 

When I rebuilt the 3.0 out of my SC into a 3.3SS, I made some CIS mods. Basically, I replumbed it to 73 1/2 specs, used a large port early SC airbox and runners and most important, added a 7th injector to richen the mixture at full throttle. I added a spring loaded contact switch to the throttle linkage so that it will activate the cold start valve when the throttle is at wot. This changes my AFR from about 14:1 (or slightly less) down to about 12.7:1. The cold start valve feeds thru a small separate manifold made of aluminum tubes so that each cylinder gets about the same amount of fuel. Not only does it prevent burning a valve or piston, it helps the engine pull hard all the way up to 7500 rpm ignition cutout. While certainly not EFI, it works pretty well and allows a lean mixture at "normal" road speeds.

Fred - From a tuning standpoint, I wish the stock rules I race under would allow something clever like this. Or an electronic control pressure regulator. But then, if there weren't those rules I'd run EFI like I do in a modified class where just about anything goes.

And I should have qualified what I said by noting I have a the frequency valve CIS system - the earlier ones don't have so many bells and whistles if left stock.

If you search for my posts on"Zenith TIN" you will find a lot of my data on afr and conditions affecting afr. also how I test under different load conditions.

Unfortunately, without load the best you can do is get idle nice.