Welcome to the site !!
2 things come to mind ..... 1st , you did not mention if you put FRESH Premium gas in it , these bikes will not run on "old" gas , old meaning over 2 months , 3 at best unless its non Ethanol (which since the jets were clogged , I will assume it was Ethanol gas in it) , so first things first , make sure it has FRESH Premium ......
2nd , it is possible that the Intake valves have zeroed or are close to zeroed out , if they are under 0.004 it will be tough to start and act/sound lean by backfiring , etc
To check the valves remove the obvious , seat, tank , valve cover ...... (it is easier if you remove the plug at this point to turn the engine over easier by hand) , on the Ignition side there is a small round plug , remove it , on the Clutch side , there is another , but larger round plug right below the water pump , remove it ....... , now turn the engine by hand until the cam lobes are facing about 2 O'clock towards the rear of the motor , ..... now look and confirm that the 2 slash marks on the cam sprocket are level with the head , the front slash should be inline with a arrow on the cam tower , and the small hole on the Ignition side should have a mark aligned , as well as the clutch side hole should have the dot and arrow aligned , all need to be aligned at the same time , so work the engine around till this is the case , along with the cam lobes facing 2 O'clock
Your valve lash should be
Intake: 0.005 , +/- 0.001
Exhaust: 0.011 , +/- 0.001
Report back with findings ......