Here I'm reaming the Throttle Spindle bush housings on a pair of 1- 1/2" SU Carburettors out to 9.5mm, for purchased split steel bushes. I've made a 6mm bore expandable pilot guide bush, to enter the worn holes from inside the 1-1/2" bore.
This is necessary to keep alignment of the butterfly disc central, otherwise there will be air bleed which will be uncontrollable.
The reamer is a 9.5mm Hand reamer, with a length of the flutes ground down to 6mm to be the pilot.
Another KZfaq video is of that process, using a Toolpost Grinder on my lathe.
I apologise for the seemingly erratic nature of events, I had the camera on a tripod at the side of the bench and I kept going out of shot, also the camera will only shoot 29mins 59secs of video due to European regulations.