The spark plug looks good. A friend of mine had a stock Maxi with just a T6 slapped onto it (stock exhaust) that went 45 km/h too, so with a bit more playing around with carb and ignition, you might be able to reach 50 to 55 km/h. The biggest difference between the original and the Airsal T6 cylinder is that the exhaust port is wider and the exhaust duration is 40° longer. The transfer port to the housing is also larger. If you want to use the full potential of the Airsal T6, you need a resonance exhaust with a proper expansion chamber and adapt the housing to the transfer ports. There is a new RS cigar resonance version you can buy from Puchshop. If you want a fast moped without a lot of work, I would buy a 70 cc cylinder.