I have a ciao with polini 63 kit including head, proma circuit exhaust, modified casings and crank, malossi variator and belt, 13 carb and I find that I can't go above a 60 jet in the carb, mine runs best with a 58 and I can get 38-40mph but it is screaming at that and you certainly couldn't hold it at those speeds for long without doing damage but I do find it's got good acceleration and plenty of power for hills and will cruise fairly comfortably at 33 though, I actually expected an easy 45 with that set up but there is no way it would ever get to that with standard gearing. I think a 70+ jet is huge for that set up and think you could possibly have an air leak somewhere, as I said mine runs best on a 58 with a 70+ it wouldn't even idle without having the screw nearly all the way in, the instructions for my kit states that it works best with jets between 52 and 56 and I find that a 58 just gives it a little more power without sacrificing top speed which to me that indicates my engine is working as it should and the fact you are on such a big jet further confirms to me you have a leak somewhere, most likely at the base of the barrel but other possible areas to check are the joint in the engine casings and the oil seal behind the points, I also had the same issue with the variator only going 3/4 of the way and I modified it so it now runs to the top but in all honesty I didn't think it made a noticable difference so I wouldn't blame that for now. I will be interested to know if you have managed to get any further forward with yours?