Have you read the article about engines in the April issue of AMA's MA?
There are some revelations there. However I don't believe they all reveal what the author really wants to be revealed.
Here are some excerpts from a letter submitted to compliment the Scale theme of the magazine, yet questioning the article, especially pages 55-57, where the author rather deposits a less than flavorful addition to a great bowl of punch. You need to read the article to get the real take on his confusion.
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Now Mr. Grxxxxxx states in his passage that the "intake ports" (BYPASS ports) open prior to the exhaust port and are closed after the exhaust ports close. Perhaps Mr. Grxxxxxx is the one responsible for several engines that I have purchased off ebay with the cylinder liners reversed. (:-))< True, I have received some good bargain engines that simply needed the liner properly aligned and they then run as they should.
If Mr. Grxxxxxx truly believes that a "Vacuum" in the upper cylinder draws the fuel from the crankcase into the upper cylinder, I challenge him to (1) remove the glow plug and attach a propeller to a normal two-stroke engine. (2) apply a fair amount of fuel through the intake venturi. (3) From just outside the propeller arc, look down into the OPEN glow plug hole and sharply flip the prop. (4) OOPs, I forgot to say to put on eye protection. (;-)) To analyze, the open glow plug hole prevented any vacuum, so could it really be that the compression of the piston's downstroke caused the fuel in the crankcase to follow the BYPASS route for its journey into the upper cylinder? Methinks so! (;-))