MOPED ARMY

All that carbon buildup is probably the result of burning excessive oil/ or transmission fluid/whatever. Clean the port and the pipe out. Your piston looks like it has some scoring, you'll probably need to look into that sometime in the near future. Almost all exhaust ports are shaped like that. The port size on the bore side has a lot to do with the power the engine makes. A larger port could produce more peak power, but you would loose power lower in the powerband. The piston ring ends prevent the port from being much wider. Wide ports will reduce piston ring life. Since it's a stock cylinder designed for a restricted moped and small children's motorcycle it's set up to produce mild power, but over a wide rpm range.