[Chris Williams]

I needs to be under load. Two ways to do it: try it on the track, check your log/recording tach, and adjust from there is the most accurate.

Or the other way. Up on stands, switch your box from linkage/undercarb to the opposite setting, press the TB button and nail it. That will put you on the stop and on the TB, check it, adjust, repeat. Just don't forget to set your box back to the correct setting, or you run will be a disaster...