i dont know if this is your issue but i had a 3pk that when i pulled the throttle 1/16-1/8 finger pull the throttle would go 3/4 open on the motor.. then when i got to 1/2 throttle the carb would go the rest of the way.. what i found on mine was a bad throttle potentiometer.. replace the trigger assembly and all worked well.. sold this radio locally to a guy and has used it for several years now with no issues...

also if you remove the carb linkage does the throttle act the same?? some times a cab sticking will cause this issue.. also a weak servo will cause this if your carb is sticking... jeremy