Leaking exhaust at muffler and head

[Kevin Blackwell]

I believe it’s a HusSeng 49cc 4 stroke engine on a beach cruiser, it’s leaking air from the muffler where it bolts to the head stock muffler only thing between the muffler and the head is a stainless steel heat shield, had no gasket before, does anyone know how to get rid of the air leaking I tried exhaust gasket and it didn’t fix it still leaks exhaust. Thanks Kb