YS91FZ quits in warmer weather
 

My YS91FZ on my UCD3D has started to quit in the air. It seems to be related to the outside temp. When it goes above 70 degrees the engine will quit at low or mid throttle. It can happen during level flight. When it is cooler in the morning, it runs great. The gallon of fuel is new (Magnum #1, 2 cycle). The plug is a new YS plug. I have tried adjusting the high end, low end, and the regulator (both richer and leaner) and can't seem to make it go away. I reset everything to factory settings today ( 1 1/2 turns out on high and low needles and flush on the regulator) and it ran beautifully this morning until about noon when it got warmer and then it quit. There is no warning. The engine just dies. This has stumped several people in the club so far. The engine has about 5 gallons of fuel through it.

Any ideas?

Chris

YS91FZ quits in warmer weather
 

Does it quit on the ground also?
What size prop and rpm?

Never heard or had problem like this with any of my YS engines.
Whenever I have a running problem, I try new check valve, fuel filter as basic. I always carry new or properly working check valve and fuel filter in my box.

Have you tried richening the idle and regulator a little and fly?

I am not sure if this is, but higher the temperature, the thinner the mixture.
Hope someone can answer better.

YS91FZ quits in warmer weather
 

Chris,

If the engine is cowled, open up the cowl some so that the engine can vent properly.

Azhar

YS91FZ quits in warmer weather
 

Have you checked your valves lately? They are noted for needing adjustment after break-in. Might waht to try a new plug while you are at it. I've seen stranger behavior from worn plugs.

John

YS91FZ quits in warmer weather
 

Overheating. More air, please :)

overheating
 

I second the overheating. MORE AIR PLEASE :tired: