I'm sorry I have been very slow in reply to your question on how I machined my carburetor. Whilst I didn't at the time have the presence of mind to photograph it I'll do my best to explain what I did.
I figured the lower section of the carburetor where the jet assembly is located would still be circular and not worn because the slide does not travel down into that area. Based on that assumption I pushed it out of the body. It was firm but came out OK. I then found a piece of steel round bar which was a bit larger and mounted it in the four jaw chuck. I then machined it so it was a tight fit into the lower carb body. I then pushed the carburetor onto it and put a dial indicator into the area where the slide ran and found it was around 0.010" out of round. Because it is a very easy metal to machine, especially with a boring bar that has been finally honed with an oil stone, I proceeded to take a series of light cuts down far enough to allow the slide to travel its full distance. Because the cuts were light, no heat was generated and it was a tight fit on the mandrel, there was no problem in turning it. I continued till it was back to true. I noted there were a few very small areas the tool had not touched but I aimed for a balance between those and avoiding taking out too much metal.
I then removed the chuck from the lathe with the job still in it and put the three jaw in place and fitted up a piece of brass which was a suitable diameter and started to machine a new slide. Bore out the centre first to the diameter of the existing slide so all the heavy machining and heat generation is done first. Then proceed to machine the OD to the new diameter of the carb body. I couldn't guarantee my three jaw accuracy when returning a job back into it so I marked jaw No1 and the stock lengthwise position very carefully then removed it and checked the fit. Prior to this I put a micrometer on the slide diameter and it was prefect along it's length. However when I pushed it into the body it was bit tight when it was deep down in the carb. I remounted the four jaw and ran the bar back in and it took the lightest skim cut. The area where the slide was tight the bar took out just a hair of a cut. Hence my reason for leaving it in the four jaw chuck from the start. There was just the slightest firmness left so I gave the two parts a very light hone with some Brasso, of course with the lathe bedway carefully covered
Now came the section where the needle is mounted on the top of the slide, and for this I used the mill to create that rectangle section. I made another mandrel for the slide to push over, this time again a very firm fit. I held the mandrel in a rotary table which has a three jaw chuck mounted on it. So again lots of light cuts so you creep up on it without it knowing what you are up to and before you know it you are there and there wasn't any sign of movement.
I'm sure there will be other people who will be able to offer better solutions however this worked a treat for me and the bike has the slowest perfect idle. It took time but it worked well.
My original question on this post regards fuel consumption has been sorted with all the help offered. It seems that the main jet may not be the correct size. I think someone must have attacked it with the drill at some stage. I'm currently machining a new one and whether it's correct or not I'm using water as the calibrating medium. As far as I understand the 160 jet number is the number of cc/min that flow through the jet so if I use a constant starting water level head with each measurement then maybe that will work??? The current one is delivering around 230 so I'm keen to see how my one is going to perform in the bike. Maybe my theories are way off but I'm open to suggestions.