Have the same engine on a Stearman and even aero tow two meter gliders with it and just checked and an APC 15x6 has done a creditable job, in fact its the original prop since I started flying it few years.back. a 14x6 sure sounds under propped to me.

I am not really a fan ot those Master K Series and if you look at them carefully in comparison to the same size APC and look at the blade planform you will find it has about fifty percent more blade area compared to the APC, Its a humongous difference. Also not convinced its just a prop problem since you said it was not the same last time. Could it not be a simple tuning problem and did you retune from two months ago? That's enogh for a season change and definitely may require a simple retuning.

John

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