I’ve encountered an issue with a YS160DZ where the engine will shut down when at WOT in verticals. Symptoms are: The hotter it is outside, the more likely it will happen. Reducing prop load reduces the issue. Again, it shuts down only in verticals. I started having the problem when the temp was about 90F or higher outside. One it hits about 100F, engine shuts off in first vertical every time.

After much messing around checking and cleaning everything, the problem seems to be vaporizing fuel in the line that goes between the regulator and the needles. This line passes the head, and rests basically against the head of the engine. Took me awhile to figure out this is what was happening, but by simply adding some spacers to keep the line from resting against the head, the problem totally went away I think. Flew 4 more times after the modification in the heat, no bubbles and engine ran great. Before it would shut down every flight on the first vertical.

My “guess” as to what was happening is as the plane slows in verticals at WOT, prop load goes up, RPM drops, cooling decreases due to lower airspeed. I.e. less cooling and engine making more heat due to increased loading. I believe this was enough to heat the fuel line in question to the point of creating vapor bubbles, which would cause the engine to shut down. This is why it never shut off in level flight at WOT, i.e. prop unloaded, engine ran cooler.

Other bits: Using CoolPower 30% heli. Flying at 1100ft elevation. Densitty altitide on the hot/humid days when I had the problem was probably around 4000-4500 feet. Prop was a 17x10APC.

Don’t need a reply, just throwing this out incase anyone else is having this problem.

This is a great post, and I thank you for sharing.

Can I send you some YS stickers? PM your address.

Thanks again,

Dave