There is really no such thing as "suck", but a pressure differential that's always trying to find equilibrium. If a low pressure situation exists, atmospheric pressure will push it's way into that place to regain equilibrium.This makes me think of how people think there is no such thing as 'suck', and that instead of negative pressure drawing fuel into the engine, that the atmospheric pressure pushes it in.
That's the reason why the reed valve is such an effective device at low and mid rpms, because at low rpms, there's more 'time' for the intake gas to be pushed back out of the crankcase, for the period that the piston needs to close the intake port. Secondly, at low rpms, there is much less intake velocity to counter the "push back effect" of gasses being forced out of the intake port on a piston ported engine.the reed valve stops the "one step back"
For this reason, high performance 2-stroke engines eliminate "intake" piston porting and have the reed valve directly installed in the crankcase. Incidently, Arrow Motorized Cycles makes a modified Chinese 2-stroke bicycle engine that uses a crankcase reed valve system.
I want to purchase that engine, but Arrow Motorized Cycles won't sell it to me; that's just their version of customer service, which still leaves me scratching my head about their business model.