A new plug is only new for 1 stroke a badly flooded cylinder can foul a plug on the first stroke. I would clean and dry the plugs crank the engine with the plugs out to blow the cylinders out. install the plugs and lay the plug wires on the plugs let the fire jump about a 1/4 inch from the wire to the plug that will give you a hotter spark. If you suspect the exhaust is plugged just take it loose at the cylinder that will answer that question. The reason the exhaust is healed on with a spring is to keep the exhaust from distorting and breaking the cylinder.