Pinasco 177 sieze after 80km/h

Hi bro....

 

I need advise from you guys...I`m ziran from singapore and i ride a P150X VLX1T fitted with a pinasco cast iron 177 cylinder block, A size piston, 20/20D si carburettor with an auto lube tank, and a sip race road exhaust pipe for daily use. The problem is when i was cruising more than 80km/h about 5 minutes the piston start to sieze even i put extra 2T mineral oil in the tank to prevent siezing..i had change the carburettor jetting at 55/160 idle jet, 160 main top jet, BE3 emulsifier,and a 130 bottom main jet.it give me extra boost but end up at 90km/h and it start to sieze again and again..... please advise...





This piston correctly assembled? arrow head towards the exhaust.

 

Ignition point? OK?

Too small carb? Compression lost?...

What does your plug says?