MOPED ARMY

Maybe a bad reed valve.

Go to this link to see how a Reed valve works. It basically should create a vacuum on the downstroke to cause the gas to be sucked into the chanber. If it is defective it will not create the vacuum to keep sucking in the gas.

<http://www.howstuffworks.com/two-stroke2.htm

It could be the reed valve or a own head gasket or defective engine gasket seals. Any of these would cause an air leak that would prevent a vaccum from being created.