Fuel - is very important to an engine - - what type and what is in the fuel ... Caster oil ... is a must for 2 stroke engines.

What you are describing is an engine over heating and seizing up. [X(] [&o]

The reason could be air flow... as suggested make sure that the air can exit the cowl for proper cooling.

BUT!!! also make sure that you fuel has at least 18% caster oil (check the manufacturer's recomendations and compare them to your fuel's ratings).

This keeps the engine lubricated and cool and prevents seizing up.