I finally had time to upgrade my Gorilla engine. I swapped the old 8,5 HP 125 ccm engine to a YX 140 ccm with 14 HP. I also upgraded the exhaust to a NHRC upswept carbon model, a Molkt 24 mm carburettor and a lightweight 540g ignition system with better power for the charging system.
Check my gallery on this build, some pictures have further description.
Here is a video of my test ride. I still need to jet the carburettor a bit leaner, and i will mount a bit larger front sprocket. The topspeed is a bit over 100 km/h on a GPS now.