Hi, well I have a PX with an original 80 cc Motor, but with a 135 DR, a 24mm T5 Carb. increased air capacity using an alu DRT spacer (I sent back the flimsy Polini Box, didn't like it at all) and of course the Venturi Kit. There was a 140 Polini main jet included with the kit, but that seemed too big, so after removing the original 108 er, I increased slowly and ended up with 120 SIP jet. This works really well, good starting (kick starter) good pick-up and acceleration throughout the range, all in all very good. I'm not that interested in top speed, however, with really pushing it I got to around 95 km/h. on a not too windy day on a more or less flat A road. Hope this helps, maybe you have solved it yourself by now.