you would need to rejet the whole fuel circuit needs to be redone.
do as the above poster said, and then test each throttle position like this.
If you want to test the main jet size - go full throttle at near to full rpm and immediately cut off your engine and pull in the clutch, coast to a stop and remove the spark plug - you should see a brownish plug - if not install a bigger or smaller main jet as necessary (I belive you know what a lean plug looks like) - then do the exact same thing at 1/2 to 3/4 throttle, this time you would need to adjust the clip position on the metering pin.
Finally do it at 1/4 throttle - this time you need to adjust the fuel mixture screw or the pilot jet size.
Doing like the above will have your carb setup nicely. What you are experiencing is loss of vacuum in the carb or too much air from the filter, the original CG125 filter is a foam piece and very restrictive which causes high vacuum inside the carb - that way fuel is sucked from the float bowl into the throat of the carb.
i do the above testing starting from 1/4 throttle - and when adjusting 1/2 to 3/4 I sometimes need a different shape needle