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Mechanical Johnson 9.9/15 Question
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<blockquote data-quote="Johny25" data-source="post: 311495" data-attributes="member: 7791"><p>Well being someone that has actually done this conversion to an 87' 9.9 I would say it is not a good idea to run it at that RPM by going to a lower pitch prop. See, the larger carburetor allows for more fuel and air to flow through the engine. And as we all know 2 strokes are lubricated by the fuel oil mix. More fuel equals more lubrication at higher RPM. Increasing RPM without that extra fuel/air is a recipe for failures internally from what I can see. Also by going over the recommended RPM of the 9.9 the engine will not be producing 9-10hp anymore....... horsepower curve</p><p></p><p> I am sure you could probably run your 9.9 at 500rpm higher than recommended for a considerable amount of time (possibly forever) before seeing problems or damaging engine, but that is only due to how solid those motors were made....not recommended though.</p></blockquote><p></p>
[QUOTE="Johny25, post: 311495, member: 7791"] Well being someone that has actually done this conversion to an 87' 9.9 I would say it is not a good idea to run it at that RPM by going to a lower pitch prop. See, the larger carburetor allows for more fuel and air to flow through the engine. And as we all know 2 strokes are lubricated by the fuel oil mix. More fuel equals more lubrication at higher RPM. Increasing RPM without that extra fuel/air is a recipe for failures internally from what I can see. Also by going over the recommended RPM of the 9.9 the engine will not be producing 9-10hp anymore....... horsepower curve I am sure you could probably run your 9.9 at 500rpm higher than recommended for a considerable amount of time (possibly forever) before seeing problems or damaging engine, but that is only due to how solid those motors were made....not recommended though. [/QUOTE]
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