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O.S. .91fsr low RPMs

Old 01-24-2016, 10:06 AM
  #1  
Skycat80
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Default O.S. .91fsr low RPMs

I have a nice condition O.S. .91 FSR I picked up a little while ago. The motor runs well, but only tops out at around 7500 RPMs. I feel like it should be hitting at least 10000, but I also realize it's a pretty old engine. It feels like it wants to be leaned out more, but even one more click will cause it to die. The only way the motor seems to be happy is with the low end screw all the way to the rich side and the high end about 1 turn out. I've checked for air leaks and don't see any issues at all. The tank and plumbing is good as it's my test stand tank and it doesn't have any issues either. With a 13X8 prop, it only turns about 100-200 RPMs slower than with the 14X8 I have on it now. I'd like to put it on an 80" space walker that I don't want to fly fast anyway, just looking for a little input.
Any help would be great.
Thanks,
Ryan
Old 01-25-2016, 07:23 AM
  #2  
Bax
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It sounds like there could be a few things. You may have a worn piston/liner fit, which means you'll need at least a new piston ring. The carburetor may have a worn needle seat, which means that the needle isn't regulating properly. That will require a new carburetor body.

You should be able to get the engine to turn in the high 11,000's with a 13 x 8 or 14 x 6 prop. If it won't, then it's not getting enough fuel and air, and likely doesn't have the compression it needs.
Old 01-25-2016, 11:34 AM
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Skycat80
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Thanks for the reply, Bax. I was wondering if there was a chance it could just be worn out. The compression seems good when it's cold, but after it's run, it doesn't seem to have a lot of compression. Also, for some reason, even after it's run for a little while, it wants a little glow fuel in the glow plug hole to start.
Time to look for something else.
Thanks again!
Ryan

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