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YS 91 AC quitting

I have a YS 91 and it is quitting on me randomly. I had this engine in another plane and retired it, no crash. I can see no bubbles in the fuel line and after it quits, a back flip of the prop starts it right back up. I am stumped... Any ideas here? Anyone with the same problem. I never had a dead stick with this engine before. I want to think it's fuel related but I can't find a bubble anywhere before or after it stops. This happens at mid low to half throttle. It will be running great and suddenly stop. Like you turned the switch off, if it had one. LOL thanks Eddie Fulmer

Reply to
Efulmer
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Had the same problem with a YS120NC. It would run all day mounted on a stand on the ground, but quit at part throttle in the air. That one was fixed by trading up to a YS120FZ. Since your engine ran well before, could be a lot of things.

Engine: You mentioned it happens a part throttle only, the midrange is probably be loading up, cooling the engine to the point where it will not fire, kind of like turning off a light switch (I used that same description when describibg the problem with my 120NC). Might be a worn diaphram and fuel plunger, or the low end needle is too rich. It is an air bleed type, in is richer, out is leaner. You check it at idle. If it speeds up, it's lean, slows down, it's rich. You could also try going in half a turn on the regulator. Reset your high speed and idle needles. How was the engine oriented in the previous plane? Upright? Inverted? Side Mounted? Did this orientation change in the new plane? Did you try a new glow plug? OS "F" is a great plug for YS engines. Is it a "high mileage" engine? Blowby past the piston can cause midrange troubles.

Plane: Could the tank clunk in new plane be folding over?

Reply to
Robert Kane

Put in a new regulator diaphagm.....couple of bucks and it'll be fine. If you have adjusted on the regulator pressure screw, return it to where it is flush with the housing.

Phil AMA609

Reply to
pcoopy

Are you running 20% or more nitro? 20/20 blend is what they were designed for.

Have you replaced the glow plug lately? I know that they are so reliable that you often forget to replace them for a year or two!

Also, check the diaphragm for distortion. If it is still flat, it is OK. If it is bulging even a little it may become unreliable.

Reply to
Paul McIntosh

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