Problem is if you are not opening up the main slide you are restricting the airflow into the carby... The manual gives the dimensions to set the stops at as shown below... these little bikes need all the opening you can give them.. 1 mm might not seem like much but it is contrary to the specs. Might be an issue with your carby rather than a general issue as when I rebuilt mine there was no sticking on the slide when set to factory specs.
The attached image shows how I adjusted mine yesterday. There is no reason to take the slide up any higher as there is no advantage. The bike is running very smoothly now. There is another slight modification I am considering. I will talk about that in the near future. Another thing I did is an oil change, replacing the unknown oil with Shell Helix Ultra. It definitely runs much cooler. Whether that is because of the carby rebuild or the oil change, I am unsure but much improved.