Bob,
You could try enriching the fuel mixture.
Ethanol gas (E10) will make the engine run a little leaner.
Make sure you have COMPLETELY cleaned the radiator fins. I like to use compressed air for this.
I would not put a foam panel under the tank. The gas is boiling because it is hotter than ~170 degrees. The foam products (I believe) will melt and possibly burn at those temps.
HTH
Keith