I Would Run It On A Test Stand With A Different Fuel Tank.If It Runs OK The Problrm Is In The Plame's Fuel Sys.There Are A Lot Of Reasons But Just Replace The Tank Copleaty. Make Sure It Is Lined Up With The Carb In The Plane.The C/L Of TAnk Must Be Close Of The C/L Line Of The Carb. Is The Fule Line Big Enought?
If It Failes.Loose Carb and Dirt Are Good Things To Try.
A Rich Or Lean Idle Setting Can Do It Too.Sounds Lean If You Must Richen It To Keep It Running.Set It Richer Then Factory Spects And Lean It Out.At Least You Will Get It Running.
Here Is Trick I Use When Working On Outboard Marine Engines.The Only Diff. Is You Will Need A Car To Do It.
If An Engine Is Running OK At Full Throttel You Can Take A Auto Timeing Light Hoked Up To A Running Car And Shine It Down The Carb With The Engine Running.You Should See An Good Spray Pattern Like A Hand Fan .No Drops Just Atomized Fuel.Just Take Care With Wires And Hold It Down So It Will Not Get A Way.
Hope It Helps.Be Careful
John