Beta 4T Pop in Exhaust

[mcman56]

I have a 2016 300 4T standard model.  It has started to produce a little pop in the exhaust when closing the throttle from small to moderate openings.  The pop is not loud but sort of echos in the exhaust.  It starts, idles and runs well but has become cold blooded so needs to run for several minutes before it will take any throttle when cold started.  I checked valve clearances and cleaned the carb with no affect.  This is with California pump gas.  Has anyone experienced this?  I'm not sure if I should go up on the pilot size or raise the needle.  Carb access is not great on this bike.