I had an LM2 and the RPM portion looked like a pain to hook up and I never did. It worked well most of the time as just an 02 monitor. When I started down the EFI road I got rid of it and bought an LC2 which is just a just a monitor. It came with a gauge and the ability to wire it into my EFI. It has worked fine so far, I will probably add another one soon.
IIRC the rpm functionis no more difficult to hook up than a tach. I like mine, when tuning I record, make changes and record again after each change this way I have a graph of each set up and can see the changes. Also I put a note on each recording with the carb set up at the time so l know exactly what I had done. After your carb is tuned you can install a gauge if you want.
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