Soon I'll be upgrading my scooter and I'd like help on what size jet to get. It's a QMB139 Chinese import, currently standard with a #78 main jet on it. I'll be putting a 47mm cylinder on (72cc kit) and a sports exhaust. I've estimated that I'd need about a #90 main jet, is this right? Could anyone give me a more accurate idea so that I can buy a smaller set of jets?
start with biggest jet and work your way down until its just right, jetting is always different for every scooter regardless if its the same make/model.
dont forget to adjust your mixture, the chinese bikes are set to run super lean to meet emmissions standards. a 4 stroke likes to run rich. there are lots of good guides on this forum
Find out what thread and size the main jet is, then go onto Ad ren a lin Ped stop site and buy a pack of 10 jets for £8.10. sizes 72 to 100 or thereabouts. then have play with jetting to get it right.
