I'm using 15% fuel, brand new that I bought with all equipment 2 month ago.
Get some more fuel from a different source it is possible that even though its "new" to you that it sat on the shelf to long
Also Montague's advice is right on follow it to the letter...
BTW 1st rule on engine care is paitence it can take a while to dial some engines in also the engine even though advertised as pre-broken in may not be and might require some running time before it settles down