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OS FS-91SII pump question

Old 06-23-2019, 06:06 AM
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Join Date: Jul 2003
Location: Bellevue, WA
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Default OS FS-91SII pump question

I have had my surpass pump engine for a while. This year I had to replace the pump as well as the regulator's valve cover as they were both leaking. What I have noticed is that the engine RPM at high end is independent of the needle screw position! More specifically I can leave the needle screw anywhere from 4 full turns down to one turn (away from fully closed) and the engine RPM hardly changes! The range that I see is 8800-9050 RPM on a MA14x6 prop and using Powermaster 15/18 fuel. Prior to the changes the ideal setting for the needle was at a full turn and I think I was getting more than 9500 RPM. It certainly was sensitive to the needle position. Has anyone come across something like this before?

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