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Old Aug 15, 2012, 08:38 AM
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Cap. take a look at the exhaust port and when the piston is at TDC note the intake port position, now rotate the crankshaft and if the intake is still open as the piston comes down that is the cause of the blowback/reversion. This is part of the overlap when the intake and exhaust ports are both open allowing the exhaust momentum to create a partial vacuum in the cylinder aiding cylinder filling. This stuff has an optimum rpm at which it all works in harmony, for example running too large a prop can make the reversion worse and running the engine faster reduces it. This is not as critical in a fourstroke.
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