Aerox problems

So I found the problem, put a new ORIGINAL belt and new roller weights (3.5g) and its very quick but it doesnt have the top speed as it should have, it only goes like 80kmh or a bit more.. Sr50s are faster than my 70cc.. And I still have the same problem, when its cold it goes even faster but when it heats up to running temperature it has less power than cold but its still better than before changing the rollers and the belt.. Any ideas on that? And also i put a little bit of extra oil in the gas tank because of the 70cc kit..