I agree Max. The R/C carbs supplied with the K series Aurora diesels are very poor.
To turn your K650 into an engine that will rival a good glow two stroke for throttle stability and clean pick up try the 5.2 mm rotor bore diameter R/C carb from a Magnum/ASP/SC .15. These are available from Just Engines in the UK.
Here is that very carb installed on my K600, which has a first class piston/liner fit. The 10 mm OD spigot is sleeved to 7/16 " (11.22 mm) OD to snugly fit into the intake boss. Just engines will make that sleeve for you at fair cost.
Idle and transition are superb with this carb.The engine will idle at 2,200 RPM as long as I wish, then pick up without hesitation or sputtering once the throttle is advanced. It had been idling for over five minutes before I started recording this video.
Incredibly easy hand starting is the cherry on top once it is sorted. I wish my PAW .35 TBR started as easily.