Aprilia SR 50 Ditech Morini 03 Cooling problem

Moin people, I hope one can help me here because I’m really desperate. The following problem: Roller runs like ne 1, starts immediately and does not make any ticking. After 4-5km it overheats however and overheats the cooling water. What I’ve done already: Cooling circuit completely ventilated. Liquid replaced. Wapu checked and functional (water comes back on top of the balance tank) head seal checked and there everything is also dense. It also loses in kei The thermostat I have temporarily expanded Do you still have ideas what I can do? Don’t want to go into the workshop with the thing because it cost me only 250 euros and I actually have enough handcrafted skills to do everything myself. Is however my first water cooled and really must say that the most exciting are Bin open for every suggestion. Vehicle details: All throttles out runs about 95 according to scooter tacho. h speed Vario Malossi Delta clutch coupling