Calling all YS91AC Experts

My YS91AC runs good above half trottle but below it gets mighty rough
down to an idle. It will actually stop if I let it run at this speed.
At idle it runs OK. All the jets are clean, one way valve is clean, no
leaks, no restructions, new plug, have not touched the regulator
adjustment except to clean it, diaphragm has a little bulge in it and
I have one on order. Tried diffenernt jug of fuel. This engine has
been performing flawlessly in my U-CAN-DO 3D for many weeks and
suddenly this.
Phil AMA609
Reply to
pcoopy
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When you take the regulator apart, you change the settings. You are just a little rich on the midrange adjustment. Try unscrewing the regulator about 1/8 turn and see if that helps.
Reply to
Paul McIntosh
Thanks for the advice Paul. I always put the regulator screw back flush with the case as they recommend and it works OK. I can't understand why after running perfectly all of a sudden it won't run in the midrange. I used these engines for pattern a few years ago amd never had to fiddle with the regulators. I put my other YS91AC in the plane and it's OK so I don't think there is anything wrong with the onboard fuel system. I'll wait for the new diaphragm to arrive. Oh well.....
Phil
Reply to
pcoopy
The other way around I think. Turn in to decrease fuel flow.
John Hawkins - From Canada's Atlantic Coast
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Reply to
John Hawkins
The regulator works in conjunction with a little plunger which has a little silicone plug at the end of it which blocks a hole, the plug can shift out of place or get deformed with age. The plunger also can get worn on the shaft in which is moves.
Reply to
John Deering
Phil-
Make sure you are running at least 20% nitro in your fuel. These engines are known to act poorly with lesser nitro contents. Also, how is your glow plug, is it new or old. Lastly, how old is the engine. If it has considerable time on it, you may be getting blow back around the piston. If so, YS Specialist have a mod that help the problem out.
Don
Reply to
Twinster2
Update: New diaphragm did the trick.
Phil AMA609
Reply to
pcoopy

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