Welcome to the site !!
I would conclude it is a clogged Pilot Jet , you mentioned not draining the gas and it sitting for a few months , that is all it takes for Ethanol gas to clog up the jets and even internal passages .... what I would do is remove the carb , and remove the bowl , I am willing to guess you will find a green coating in the bowl , that is the Ethanol , and means the carb needs the complete cleaning , and I would personally just replace the Pilot Jet , they are inexpensive and will eliminate the worry of if you got the old jet clean or not ..... remove any rubber items before cleaning with any carb cleaner or carb dip ... it will eat any rubber ..... make sure to remove the fuel screw , it will have a spring , flat washer , and a O-Ring , in that order , the O-Ring sometimes gets stuck down in there when removing the screw , so you need a pick or small tool to remove it before cleaning
Before you put everything back together , drain the tank , and put in FRESH gas , if the bike is going to sit for more than 1 or 2 months , DRAIN the tank , and either run the bike till it runs out of gas , or drain the carb as well ...