CO Test Problem


I am posting this for a member of another board. I have been told that he has a bone stock American specs 2006 Busa. He is stationed in Japan and is undergoing emissions testing. It was tested in Japan and the CO level was a little to high (see below). During his idle test his CO level was within standard. The test was done in Tokyo and the kpa was at 99.9 which is very close to sea level.

Below are my test results/then the Japanese standard.CO: 22.23 / 20 (Fail)HC: 1.628 / 2.93 (PASS)NOx: 0.115 / 0.51 (PASS)

Do think leaning it out some via a PC or reflashing the ECU would help?


Take it back to the factory.
It is right there. :laugh:

I don't know what a guy would adjust to fix CO emissions. ???


Donating Member
higher co levels indicates an over rich A/F ratio. If it's close to passing then do as mentioned, pull the air filter. Sounds like a little fuel triming is needed.


Take it back to the factory.
It is right there. :laugh:
Now that is funny.

Thanks for the replies all. Makes sense about the air filter and leaning it out. How do you think it is best to lean it out? Am I on the right track by suggesting a PC or reflashing the ECU? This guy has to get the bike from Misawa to Tokyo each time for the test and that journey is not cheap so I hope he can pass the test sooner rather than later.


I have another question concerning this problem. This is a 20 minute test at a moderate RPM level the guy failed down in Tokyo. I could see if the filter was dirty that more fuel would be used. What if the air filter was completely removed just for the test? Or the small airbox mod done. Both mean more air but would the bike learn during the 20 minute test to adjust fuel due to more air?

Thanks in advance to any replies.

Mr Bogus

Trouble Makers Inc.
Donating Member
never had much luck pulling air filters on "FUEL INJECTED" motors... (well unless the thing was just plugged solid) Also, is this a "cruise" test? Idle test? or something like the old IM240 test where it is road tested on a dyno for all condition?

CO measures burned fuel in the gas, HC is unburned fuel, NoX is a by product of high combustion temps

The motor is just rich.. (20? or is it 2.0/.20? 20 is off the chart, 2% is more likely) not sure what the tipping point is on these motors but as that number goes down, the Nox is going to start rising and at some point and you go "over lean" the HC's will start to climb after falling initially..

The 02 sensor on the Gen2 takes care of all this at anything less than full throttle..

vacuum line to MAP bad or leaking *(or bad sensor, but not likely, they are pretty reliable)
leaky injectors or excessive fuel pressure
improper mapping (most likely cause IMO)
excessively nasty oil in the crank case
Charcoal canister malfunction (saturated)
low idle speed

Sometimes you can just create a vacuum leak (after the throttle bodies) and that will lean a motor enough to get them to pass (you need a gas analyzer for this little trick)


Thanks Bogus. I guess the problem looks more complex then just leaning it out. The owner says the bike is totally stock. Since this is the case I guess dirty oil or something faulty could be the problem. From what I understand this was two part test. The idle test was passed but this 20 minute test is what failed.

I have attached the pdf of the failed test. I had it translated so it may have some minor errors. I am not sure at what RPM range the bike ran at during the test.


Mr Bogus

Trouble Makers Inc.
Donating Member
actually all it appears to need is a bit of "leaning"..

Now I may be reading this wrong but it appears this is a Gen2 bike and it was only tested at idle.. I do see the 20 minute run.. curious... does a person run the throttle? (this could contribute to a "fail" and sometimes just retesting results in a "pass")

The idle speed was right at 1100 rpm so that is at the bottom of the scale.. He needs a shop at this point with a gas analyzer and make a couple small tweaks

Calibrate the TPS
Idle speed (raise a bit)

watch the CO/HC's you want the CO to go down of course but only as long as the HC's go down with it.. I am guessing this bike should have a catalytic converter so NOX and HC should never go up.. (they are consumed in the cat)

IF i was doing this (and cheating) bump the idle, back down the TPS and if need be, take the line where all 4 intake ports are married and create a small air leak :whistle: (enough to raise the idle about 100rpm)...

This really is tough work for a DIY guy and my guess is that there should be a list of shops that the emission testers should have to get work done at....

I suppose it is possible to plug a PC in and just have a leaner idle setting built right in.. flashing the ECU really would be the ideal fix provided Idle and TPS adjustments do not fix it..


This is a 2006 model. There is something about 50km/h at the bottom of the first page so that is what they may have ran the bike to get the readings. I am not sure of what gear it was in.

Thanks for your thoughts. Until this guy finds out the true details of the test we can only continue to speculate. If there is something that needs to get checked out then since we are in Japan then you would think that would not be an issue other than it being a US spec bike. I am just glad that mine was manufactured before 01 APR 2001 and didn't have to go to Tokyo for these test.



due to the stumbling mode while driving in stock layout in lower rpm, allmost all of the Busa drivers here in Germany enrich the idle up to 5% (normally 2%). I usually do it with the Yoshi box as it's easier to maintain than to reflash the ECU.
So I'd suggest just to lower the idle mode (which works up to 10% of throttle) by, well, 2....5%, then get the testing done and enrich it again.
Should work.
At least it does with German Busas :-)


Mr Bogus

Trouble Makers Inc.
Donating Member

due to the stumbling mode while driving in stock layout in lower rpm, allmost all of the Busa drivers here in Germany enrich the idle up to 5% (normally 2%). I usually do it with the Yoshi box as it's easier to maintain than to reflash the ECU.
So I'd suggest just to lower the idle mode (which works up to 10% of throttle) by, well, 2....5%, then get the testing done and enrich it again.
Should work.
At least it does with German Busas :-)

am guessing you mean the idle portion of the "map" for fuel curve? (corrects a lean tip-in stumble)

adjusting the idle speed would affect the TPS but not sure how much it is going to modify that fuel curve by 5%
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