The Jets are the same for both the 70 and 48 engines and are 0.70mm or close.
The 70cc needs a bigger jet for sure. Luckily the jet unscrews from the pin fuel well inside the carby. Even luckier still Dellorto PHBG Main jets are a perfect fit!! and cheap at only $5.
I would try a 0.78mm to 0.80mm or for the 48cc engine and 0.80 - 0.85mm for the 70cc engine. You may have to compensate by raising the clip on the pin.
Very handy that the Chinese engineers thought to match the jets with Dellorto's
Dellorto PHBG Main jets - Google Search 
