Check the spark plug. It should be a light brown color, not fouled with oil. Check the exhaust outlet to make sure it is not plugged. Finally check the cylinder for compression. Your rings may need to be replaced.
Mosquito has a flat or worn tire.
To change a punctured tube or worn tire remove the axel. A 13mm bolt holds on the drum brake. Four 10mm bolts hold the two sides of the wheel together. Remove them and split the wheel. You can then insert a new tube or patch.