Hello

my setup : dz160 ,18.1x10 prop, cool power 30% fuel.

Description of the problem:
After a year of not Problems Flights , Yesterday I flew a my Seniors series,
At the end of the series, after about 6- 7 minutes There is a vertical climbing.
Twice I got exactly in this Climb Stop engine.
After landing, I saw that in the fuel tank There are about 1/4 tank fuel (no fuel problem)
I checked the fuel line in the tank and it look good (I use the special ys clunk )
Do you have any ideas for this issue ?

Thanks
kobi