So I finally got this set up (was injured for a while and not able to do karting stuff). I had a bung drilled and welded into the muffler by a local shop (it's easier for me to swap out the muffler). The AIM lambda sensor requires an external power supply to heat the probe before the engine is started - so I had to get a 12v battery with F2 terminals and strap this to the kart (I was not crazy about this but when we did our testing there was no one else on the track).
The data were interesting. The display can be set up on the MyChron so the data is visible in real time to the driver, but to recall the data I had to download it to a laptop at home (did not want to lug a laptop to the track). The lambda data is spiky - so I overlayed 2 or 3 laps at the same time to smooth things out and throw out outlying data. We had a lambda in the .80-.89 range which I think is good? The air density at the track was about 100% which is high for our area. We ran blue slide, clip on 2nd notch from the top, and had the float around .900. To get it to idle I had to turn the air screw all the way in - even a little bit out and the engine would die but it ran well - no popping or backfiring and my kid reported good power. I might drop the float level a little if the air density stays like this for the race and that may allow the air screw to be backed out a little.