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Exhaust Gas Analyzer

Part 1

Date: Tue, 14 Sep 1999 22:18:08 -0500
From: Fred Harmon
Subject: Exhaust Gas Analyzer readings

In an attempt to end the guesswork of setting my mixture screws, I recently went out and bought an exhaust gas analyzer. I had previously read a couple articles in Rider about them and decided it was worth a try.  $190 later I am the proud owner of a Gunson portable EGA.

The first hurdle I had to overcome (besides the checkbook) was accepting the fact that I was going to have to drill holes in each of my four exhaust pipes (I think I can now safely say I have truly gone over the edge, drilling holes in my bike!!).  Once the dastardly deed was done, I could now "sniff" each cylinder and set the mixture screws (via a right angle motion pro screwdriver) for the ideal 14:1 ratio (3.8 percent Carbon Monoxide [CO]).

Well, if you have trouble synching you carbs, don't even think about doing this. The analyzer is a finicky device and requires constant attention and re-calibration. The readings seem to float around a bit and it is difficult to get a constant reading. I found I got the best results working outside in open air with a fan on the bike and analyzer. That helped keep the bike cool and the analyzer with a clean air reference sample for the collector.

Once I got the hang of using it, I did some initial measurements.  With a K&N filter, and mixture screws at 2 1/4 turns from seated I was getting mixture readings ranging from 6.6% to 4.5%.  All four cylinders were at least a full percentage point apart from each other and WAY too rich.  I took the K&N out and put in my Uni foam filter, and the readings all rose by about one percent. WAY WAY TO RICH (#4 cylinder read almost 8 percent CO!!!!

So I started turning screws.  I started at one turn from seated and worked from there, setting each cylinder at 3.6% CO.  Oh, I forgot to mention, before I ever even thought about doing this, I first did a full valve adjust, carb synch, and spark plug replacement, and the Gunson manual also confirmed that this all needs to be done PRIOR to making any mixture screw changes.

Anyway, once I got all done, I immediately noticed the bike "seems" more responsive to throttle inputs at idle and has less vibration at 4K rpm, although I haven't actually ridden it yet. I have got to go to the hardware store first to get some screws to plug the (cringe) holes in my headers. I drilled the holes with a 7/32 bit and tapped them with a 6mm tap so that fairing screws would thread into the holes. I will get some standard 6mm bolts to plug the holes. Hopefully by tomorrow I will know how it actually rides.

I also went back and reviewed the original factory settings of my mixture screws (that I recorded three years ago when the bike was new). Low and behold, the original settings were not all that far off from what I came up with (except for #3 carb which was 1/8 of a turn from seated from the factory).  All of the settings ended up in between 1 turn from seated, and 1-1/2 turns from seated.  My 2-1/4 turn settings were way to rich even for my K&N filter!! And all four cylinders were far apart in their CO values, indicating that setting all four screws out a certain number of turns is not really a good way to set up the bike.

I don't yet know if the 3.6% number I choose is the right one or not (will have to do some more "experimenting") but I suspect that having all four cylinders at the SAME value (or mixture) will have a dramatic reduction in vibration. Just running the engine in the garage at 4K rpm, it seems much smoother already. And I haven't even gone back to re-synch the carbs yet either...

I like this EGA tool.  It is "fairly" easy to use once you get used to its quirks. It is also nice if your bike is not running right because you can stick the EGA up it's exhaust pipes and easily cut the problem in half determining if the problem is from cylinders 1&2 or 3&4.  And if you are brave (crazy) enough to drill holes in your pipes, you can further isolate misfires to exact cylinders!

Interesting side note.  After drilling the holes in the pipes I could see blue flame flashes inside my headers, I think from the fresh air entering and mixing with the hot exhaust gases.

Hopefully I'll have more to report in a week or two after I get it all "dialed in", but judging from what I saw tonight, I "think" 2 turns from seated is too rich, at least at my altitude anyway (1,060 ft above sea level). 1-1/2 (or even 1-1/4) appears to be closer.

And no, I am NOT running reformulated (MTBE) gas....
Fred Harmon
Madman at large

Part 2

Date: Wed, 15 Sep 1999 18:55:20 -0500
From: Fred Harmon
Subject: Mixture settings (YeeHaaa!!!!!!)

I got the bike buttoned up and went out for a ride after setting my exhaust mixtures at 3.6% CO.

Wow!!  The bike is SOO much SMOOTHER!!  No perceptible buzz in the 4K rpm range, and 6K and 8K are soother as well.

The bike is a bit harder to start and needs more choke.  I also get more heat around my feat, telling me it is running hotter. However, I have better throttle response and it feels like more power, despite having removed the K&N filter and going back to a foam Uni filter. I did get some "hunting" in the 2Krpm range.

In retrospect, I think 3.6% is just a tad too lean for this bike. I plan on going back in and re-setting them all to 4.4% or maybe 4.6% later.

I think the big change I felt is from having them all set evenly. It seems to have made the bike run much smoother. Almost electric. Didn't even feel like a Concours without the normal buzz at 4K.  Looks like this is the ticket to truly de-buzzing the Connie.

Stay tuned, more testing to come....

Fred Harmon
Mad Man across the water (been breathin those fumes too much)

What Fred didn't mention was how to get the EGA probe into your exhaust. Because you need to test each cylinder separately, and the Connie has a 4 into 2 exhaust systems, it's not that easy to do. What I have seen suggested elsewhere is to drill into each exhaust header, just down from where it exits the head. In order to close the holes, but still have them available for future use, there's a product out there called a Rivnut. The Rivnut EZ seems to be the right model as you don't need access from inside the tube to secure them in place. These are inserts and then a bolt threads in to close things up.

From: COG ListServ

August 2001 

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