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YS140L Riddle

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Old 06-16-2003, 11:20 PM
  #1  
woodie
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Default YS140L Riddle

posting this for a friend who is internet challenged... First a little background. YS140L with approx 375 pattern type runs on it. Ran beautifully. Put in new plane with following symptoms. Start up, idles well at 22-2300 RPM, runs strong at 86-8700 RPM with APC 15X12 (all this on 15% Magnum fuel). Throttle back, engine drops to 2200 RPM then increases to approx 3000, stays there for about 30 seconds then gradually comes back to 2200. Replaced check valve, exhaust system, throttle servo, no change. Fuel system is holding pressure. Tried new piston/ring/sleeve, no change. Valves adjusted right, tried different fuel, plug, same thing. We are definitely puzzled on this one. Any ideas?

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Old 06-17-2003, 11:02 AM
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Default YS140L Riddle

Did you try replacing all the piping and cleaning the filters. I had a similar experience at full throttle, that went away when I replaced the piping.
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Old 06-17-2003, 01:05 PM
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yes, replaced entire fuel system including the check valve......
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Old 06-18-2003, 03:30 PM
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Dave Shadel
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Default YS140L Riddle

It could be an issue with the disc valve. After this many runs, the backplate surface might need to be lapped and the disc valve reset.
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Old 06-18-2003, 03:47 PM
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Default YS140L Riddle

May I suggest something that hasn't appeared here? All YS's are nitro hogs. Try running 25 to 30% and you will find that you'll have your old engine back. Before you poopoo this please keep in mind that my LHS was the testing ground for Sean McMurty, TOC and world FAI flyer. He flies his YS's elusively on that high of nitro.
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Old 06-18-2003, 04:06 PM
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Dave Shadel
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Default YS140L Riddle

Good thought, but he ran 375 flights with 15%, no problems.
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Old 06-18-2003, 05:29 PM
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Default YS140L Riddle

actually he did try higher nitro fuel, same result. We finally ran out of things to try and he sent it in to let the YS gurus have a shot at it. thanks for your suggestions, it will be very interesting to finally figure this one out.....

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Old 06-22-2003, 04:57 PM
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Just got a call from my friend in reference to his YS140L problem discussed in this thread. He talked with the good folks at YS service and they diagnosed the problem as the crank spinning in the bearings causing the engine to overheat. Sounds reasonable since we know heat causes strange things to happen in these engines. The engine should be back in the plane in a cpl days (nice turnaround!!) and we'll let ya know how it goes.... Don
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Old 06-22-2003, 10:44 PM
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Dave Shadel
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I think he meant spinning in the case, not on the crank. We have seen a few where the rear bearing bore in the case is too big and allows the rear bearing to spin in the case. A loose fit of the crank in the bearings will not cause this problem.
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Old 06-24-2003, 09:47 PM
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sounds logical, sorry for the misleading post...... Don
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Old 06-24-2003, 10:14 PM
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Dave Shadel
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No problem. Let me know how it works out.

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