This spring I bought a used "Innovate Motorsports 3844 MTX-L Complete All-In-One Air/Fuel Ratio Gauge Kit" from Amazon for $130 and it saved me weeks of troubleshooting. It was sold as used but it was new in the box.

The cable is long enough to to bring it in the car for "live" tests. I rigged a magnetic mount and set the entire thing in my ashtray while I drove it. I agree 100% that "live" tests are the only way to go.

Once I was dialed in, I put it in a box and it sits right here beside me! This setup is cheap and it came with computer connections so you can record the readings are regular intervals. Combine that with a timer and you can chart your results.

It would take very little to convince me to sell this setup now that i am done with the carb work!