This is a Mikuni slide as it does have the Mikuni symbol next to 2.0

I had tried some light sanding without success. I coated the slide with magic marker as suggested by HunterDave and found that the carb barrel had slightly "ovaled". I sanded the high areas and voila, it slides up and down easily now. Thanks Dave and everyone else who responded.
Hopefully I didn't oversand...........

What grit paper did you use??

Be careful sanding down there as the guide pin sticks out. Great though if it's now sorted. Heavier spring for safety might be a good idea as the spring is very light due to having the oil pump spring to contend with as well when twisting throttle.

320 grit then 600 grit