Here is a great forum with detailed repair manuals for rebuilding carbs and more:
https://www.smokstak.com/forum/forumdisplay.php?f=1
Mechanic in a bottle solutions seldom work with gummed up carbs. As others noted there are tiny passages in the carb that must be manually cleaned with tiny brass wires or other means (being careful no to damage the orifices!).
Also I recommend you clean the slip rings if the genny has sat a long time.
This is why it is critical to run these gensets every month, and let them run for a half an hour under load so that the heat and vibration can help agitate the fuel inside the carb and help keep it clean inside.
These things do not tolerate sitting well at all.
