I suspect you’ll find the problem in the tank. Brand new = possible chunk of plastic from the molding process floating around; or something was stuck to the clunk or fuel line and got inside the tank when you assembled it.

My brother had a new plane that developed similar symptoms. It was fine the first couple of trips to the field, then started the deal where it would run fine for a few minutes then die. He was tuning the engine every way possible and the problem wouldn’t go away. Someone suggested taking the tank apart and he was positive that it must be something else because the tank and everything in it was new. He finally pulled the tank and found the clunk had fallen off the end of the fuel line and was just rolling around in the tank. When the loose end of the line floated above the fuel level it ‘ran out of fuel’ and died. Put it back on, secured it with a tie wrap, now it runs fine again.