It's not uncommon for used bikes to work briefly then die. This is caused by crap in tank taking their time to work their way towards exit and clog petcock and filter.
So in addition to carbs, pull petcock and rebuild it with K&L kit.
Also fish out internal filter from fuel-hose between petcock and carbs. Toss it and replace with external filter that you can inspect easily to determine amount of debris collected and replace as needed.
