Sport_Pilot,

The sleeve valves in a two-stroke, unlike popet valves in a four-stroke, (but like a rotory valve in a four-stroke) open very quickly. The piston is speeding down and unlike a closed popet valve, it doesn't have to accelerate to open (the valve). That would put things closer to your description.

Still, a two-stroke doesn't start the comperssion with a full load of mixture, due to bad scavanging.

Sincerely,