Hi Alexander, welcome to the forum
I noticed your love of a Honda 4 stroke running through gears.
I run a GX35 running through a standard 9spd cassette , Ive run over 1000ks in the last 3 years, with no problems. (I'm only 10ks from work.) Its great having that range of gearing.
Hard to believe you only get 60k's to the litre with the 31cc. I worked out I get over 90kpl although that is on the flat, traveling at 50kph.
By the way, I love old scool GT's, I have a 2 stroke LTS also. Do you have any pictures up yet?