af

Have to carbs all of the sudden when I turn the af srew all the way I or out has no affect is there somthing plugged

I was looking into purchasing an AF meter ( portable ), I have been looking into several kit available...However I'm a little confused about it. They all look like they have weld in 02 sensors?? Can I just place them in my exhaust pipe and measure that way? I really dont wanna be welding...