Using exhaust O2 sniffer

I had a chance to use a O2 sniffer we use at work to tune different combustion processes.

I have a bike that I thought ran very well. All free mods, PMB insert. JD kit various jet adjustments etc...

After verifing the unit was cal'd up and the engine warm I had a exhaust O2 of over %17.5 at high idle. That's still pretty lean. Ideal should be below 14. I was able to dial it down to just below %15.5 with the ZT fuel screw at 2.5 turns out.

Ambient temp was just over 60 F Sounds like I need to richen it up a bit. Especially since I hope to have a new silencer by the weekend.

Pretty cool to make adjustments and see it right away. The only problem I had was on the stand I eventually got too hot and lost some coolent thru the over flow. Its fairly small and battery powered, I'd like to find a way to get some reading while loading the engine up a hill or something.

Just some info...

how far did you have the probe down the pipe?if you didnt have it at least 24 and preferably 36 inches in there,you got false readings.

if it was 17.5 it would not have been idleing well at all.

The probe is approx 16 in long. Why would this be a problem?

Are you saying that is not long enough because of the baffels in the stock pipe?

I can see nowhere that O2 could get in the exhaust system from outside the combustion chamber. The gasses in the silencer should not be resonant but instead should continue to purge from the header pipe.

The analyzer has a internal metering pump so you don't need to rely on exhaust pressure to get a good sample.

I did use it on my Harley and got reading I expected (around %13).

I'm going to try a few things tonight to keep the bike from over heating. I have a high volume fn we use to keep out horses cool in very hot weather. I'll set it in front of the bike to get good flow across the rads.

yes,i know it has a pump.

however,with the baffles and you only being able to get it 16 inches down the pipe,fresh air is also mixing with the exhaust.

I thought that is what you meant. Thanks for the feedback.

I can't see how fresh air is getting back into the exhaust silencer 16-in in while the engine is running. There is a positive perssure inside and with a measured temp of 280deg + and the expanding gases how could this be?

I've installed head pipe fittings for EGT probes on 2-strokes and without installing a tap in the head pipe for the sniffer what is a better way to do this?

Thanks again

Burned now that we got you here would tuning by maximizing CO2 output be a better indication of combustion or the ratio of CO2 and HC be a good indicator? all this is only good for idle mixture without loading it on a Dyno or maybe you might be kind and give up a trick or two Thank You

At idle, CO should be between 3 and 5%, HC should be well below 300ppm....

I'm going to give this a again this week with the pipe mods and new jetting.

Thanks for all the input, for those interested I'll post what I find.

At idle, CO should be between 3 and 5%, HC should be well below 300ppm....


we are talking 2 different ways of measuring exhuast gas int his thread.

when measuring CO% it should be 3-5% at idle, 2-4% at steady throttle and 4-6% at wide open throttle.

when measuring actual air/fuel ratio it should be 13.0 to 14.0 at idle,14.5 to 13.5 steady throttle and 12.8 to 13.3 at wot.

these are not absolutes,but i find them to be pretty much constant on naturally aspirated motorcycles.

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