Cheapest O2 kit?
 

For those who have a carburetor and need tuning, is there like a cheap kit, that you can buy, where you can just slide an O2 sensor in your exhaust pipe, and measure the A/F levels?

Most of the kits require you to screw in the O2 sensor in the exhaust pipe. But most scooters/motorcycles have no provision for that; and I don't want to damage my exhaust.

Those kits are all $100+ kits...

Any other solutions?

I used to have a exhaust reader that slid down into the exhaust end to read Lamda and air/fuel ratio. It was ancient and huge but worked great. I sold it and kinda regret it now. I know Koso sells one but I don't recall if it bung attached, like you are trying to avoid, or if it slides down into the exhaust end.

The reason they mostly use the bung attachment is because modern exhaust use catalytic exhaust and any reading after the cat will give a false reading if read after the cat, hence the bung before. The exhaust we used our old school one on were expansion chambers on 2-strokes. No cats in those.

If I tune now I just do plug chops. It's time consuming and annoying but it works. I'm in the process of putting a bigger main jet in my Buddy 125 when I get off my butt.