The exhaust gas analyzer

[mikenixon]

I want to celebrate the exhaust gas analyzer. Interestingly, of the Big Four motorcycle OEMs, only Yamaha ever formally embraced EGA use. But that doesn't mean motorcycle repair shops have been as hesitant. They use it to tune engines, for troubleshooting, and of course for preparing vehicles to pass state-mandated emissions tests. It's a powerful tool.

Although five-gas EGAs are the norm today thanks to catalytic converters and air injection, the earliest machines measured just two gases: CO (carbon monoxide) and HC (hydrocarbon). But don't underestimate the power of the two-gas tools. CO and HC alone are more than sufficient for vintage tuning and troubleshooting needs.

So let's look at how to use the EGA, starting with CO measurements. First, just what are these two gases, CO and HC? Whereas similarly-sounding and harmless CO2 (carbon dioxide) is two parts oxygen to one part hydrogen -- CO, at a ratio of one-to-one, is by contrast oxygen-starved and that is the key to its importance. When the CO is abnormally high, the burn is happening, it just isn't the right mix; it lacks air, it's rich. So CO is essentially richness. The other two-gas analyzer's measurement gas, HC, is quite a bit different. It doesn't speak of incorrect mixture the way CO does. Instead, HC indicates significantly interrupted combustion. A lot of fuel has made it through the combustion chamber and into the exhaust without even being burned. That's HC. So CO means too little air, and HC means interupted burn. Got it? Simple.

So what are the proper amounts of each? 1970s through mid-1980s four-stroke Japanese motorcycles are designed to emit between 2 and 5 percent CO, and from 400 to 800 PPM (parts per million) HC. The numbers go down drastically after 1985 with many engines squeeking out just 0.5 percent and 100-200 PPM going into the late 1990s, and falling even lower after that.

With high CO readings look for too-rich pilot screw settings, a dirty air filter, high float levels, or leaking float valves. Also, the needle jets may be worn, or the choke plungers may be leaking or the carburetor's air bleeds restricted.

Interpreting high HC readings is a bit more work. The key is to simultaneously view the CO. When the HC is high and the CO is normal, ignition misfire is indicated. If the HC in this scenario jumps upward periodically with the CO dipping correspondingly, the misfire is due to intermittent ignition. On the other hand, a high HC reading accompanied by a lower than normal CO reading is still a misfire but may be either air/fuel mixture related or ignition related. Determine which by very slightly applying the choke, or by taping up part of the air filter. If the CO increases, the ignition system is okay -- it is demonstrating it can support combustion. The fuel system then is at fault and is creating the misfire. And finally, a high HC reading accompanied by a high CO reading plainly is caused by either mechanical or fuel system faults. Ignition is fine. The ignition system is okay because, yup, the high CO verifies that it can support combustion. Simply perform a compression check on the engine to distinguish between mechanical and fuel causes for this high HC.

Neat huh? The exhaust gas analyzer. An incredibly powerful tool that despite its history on the automotive scene is under-appreciated by many in powersports. The EGA's troubleshooting and tuning potential is huge.

[77Gowing]

Great article Mike.
Wish I had this to share with my 4h science fair student in his project.
I was his advisor and his goal was to make an exhaust filter. I was not allowed to work out all the details even though I found the approach crude. I had to advise and let his research teach him. Anyway, he made a filter out of activated charcoal
And stain less steel mesh. He placed his filter in my 2009 Scion xB exhaust and we just did idle tests. His premiss was that with the filter CO would be reduced.
We used a CO sensor and made measurements without the filter vs with the filter.
The data did show a significant reduction, but only for a short while as his filter began to saturate. He took 2nd place in Texas state 4h science fair.
Regardless how he placed I feel it was a success in that he learned a great deal, even though the solution was not very practical.
His initial desire was to "make a fire proof exhaust filter.". Initially he had no knowledge about exhaust gas component species, and had no idea what was going to be filtered out. He assumed he was going to filter "germs" lol.
Anyway he learned a great deal throughout the process.

[mikenixon]

Great article Mike.
Wish I had this to share with my 4h science fair student in his project.
I was his advisor and his goal was to make an exhaust filter. I was not allowed to work out all the details even though I found the approach crude. I had to advise and let his research teach him. Anyway, he made a filter out of activated charcoal
And stain less steel mesh. He placed his filter in my 2009 Scion xB exhaust and we just did idle tests. His premiss was that with the filter CO would be reduced.
We used a CO sensor and made measurements without the filter vs with the filter.
The data did show a significant reduction, but only for a short while as his filter began to saturate. He took 2nd place in Texas state 4h science fair.
Regardless how he placed I feel it was a success in that he learned a great deal, even though the solution was not very practical.
His initial desire was to "make a fire proof exhaust filter.". Initially he had no knowledge about exhaust gas component species, and had no idea what was going to be filtered out. He assumed he was going to filter "germs" lol.
Anyway he learned a great deal throughout the process.

Thanks for sharing that, 77Gowing. I did not know a filter could be used that way. Interesting. It reminds me of something. Kawasaki was having trouble on its supercharged watercraft with water entering the engine on engine shutoff (personal watercraft like other inboard craft have water-cooled exhaust systems). It was so bad the spark plugs were corroding into the head and breaking off when trying to remove them, and cylinders so wet the engine would not restart for half an hour. Their solution was a stainless steel honeycomb filter, or as I called it, diffuser. It worked but had to be replaced if I remember correctly every 100 hours as it eventually burned through.