Engine braking a 2 stroke will destroy the engine. That is why there is a freewheel mechanism in most (all?) 2 stroke cars. The engine oil comes with the mixed fuel in a 2 stroke, and when you engine brake no fuel goes to the engine, when no fuel goes to the engine then the engine will not get any oil as well, and no oil to the engine means no lubrication of moving engine parts - which in turn leads to a ruined engine. The freewheel mechanism on 4th makes it so that the engine always gets fuel and lubrication, therefore it is ok to "engine brake" on 4th geat but not on gears 1, 2, 3 and R. This makes driving a trabant more...interresting.