Geziz Christmas, folks. I mean. Wow.
And Merry Christmas, too.
A pump, by definition, is a device that either uses suction OR pressure to move liquids or gases. So, absolutely, ALL 2 strokes operate like a pump(as well as many other mechanisms folks here are saying are not pumps or vacuums), and they all act as though they are supercharged on the transfer intake side. If a device uses standard air pressure to fill it's cavity, it still is using suction as, by definition, it only has to produce a partial vacuum VS an absolute vacuum to be called suction. A partial vacuum simply means it has less pressure than the air around it. If there were no pressure differential, then no fuel, mix, or air will exchange. At least not in a timely manner(which is how it can be painful it to operate a saw at very high altitudes). You need a pump to create that pressure differential. Thus, even though it is using 14.6psi at sea level to help move the charge, it is still using suction. It's just not supercharging the mix on the intake side. Without behaving like a pump, there would be no pressure differential. And without being a pump, neither air nor fuel nor oil nor strato nor whatever would move through the engine. A good hint is the fact that two of the strokes of a 2t engine are called a 'compression stroke'. Another hint is the fact the freaking thing has a piston in it. According to the 'Two Stroke Tuner's Handbook", average crankcase compression is 1.5bar on most modern two stroke engines - supercharging a fuel mix means more than 1bar of pressure. Thus, the intake phase for the transfers is supercharged unless they open too early. That is probably where the confusions about pumping and sucking comes from. A charge does not need to be supercharged to be pumped...or sucked. And once that mix that's been all pumpy pumped and sucky sucked explodes, it starts to create it's own pressure as well, shoving the piston down. Since that piston goes both down AND up, it will definitely displace volume that will be filled with an incoming charge as it races back up, creating a partial vacuum, aka a pressure differential, AKA suckin' or suction.
So there's more pumping and sucking going on in your average 2 stroke than a first year college dormitory.
This is how stratos work; It takes the deference in pressure to fill the top of the transfers to help with scavenging. It doesn't supercharge that strato charge, though. Otherwise you'd end up with too much air and too little mix. At least how the ports are currently designed.[/B]