Yamaha 2 strokes are made to very good tolerances but we always used 50:1 on the larger Yamahas.
This is going to be a copy of something Chinese or North Korean
Run it on 25:1 but I wouldn't spend anything on it if there are problems. Does it pump water
btw it might be air cooled like a Honda
I sold my Johnson 3.5hp during the winter after 13 years and bought a Honda
2.3hp for similar reasons you have bought the Gull. But with the nice weather
in the UK it's completely the wrong time of year to buy something really good without paying through the nose.
Give the Gull a go and it can always go back on e bay if its a problem.