I don't think there are any slides as such in your carbs. They are butterfly and diaphram operated. Islander must have still been thinking of the old concentrics or Del Ortos and leading everyone up the garden path (or down memory lane perhaps?)
I don't know how the cold start system works on your carbs, but wouldn't it be logical for the handlebar control to be a bit "stiff" to hold it's position?
I get on much better with silicone when lubricating plastic parts. I think WD40 is inappropriate. "Mr Sheen" is laden with silicone and has often done the trick for me with sticky plastic parts.
__________________
|