Keeping this brief. Spec of scooter is px125 MY 2003 with DR177, 24mm carb.
I had a sip 2.0 road on it which drove fine but the exhaust was a couple of years old and passed it best, had become rusty and very noisy. It was jetted to 116 main and was spot on with plug colour (running on an NGK 8 short reach plug, so cooler. I was hitting indicated speed of 110 kmh and always without fail got 105. The GPS revealled top speed as 63 mph
So, a polini box was put on it. Upjetted to 118 main. When i checked the plug it was rich. So ive taken the plug down to a 7 short reach. Still the plug colour was too rich so taken jet down to 116 and now the colour is fine, albeit a tad rich on the pilot circuit. Due to winter weather i have only just gotten around to giving the scooter a thrashing with the polini box on. Its a great sounding exhaust, more like the original, sounds a bit like a p200 now and the torgue and pick up are very good; its particularly good at 50mph overtakes, really punchy, more so than the sip road 2.0 It flies really quickly up to an indicated 100kmh which on the GPS was 57.5 mph however it will not push over 100kmh (new speedo cable and drive worm also fitted).
When the scooter was a standard px125 with the sip road 2.0 i would regularly see 105kmh indicated so although i have a lot of power with the polinibox i cannot get the top speeds i was getting before as 125cc and 177cc.
Is there anything im missing here? Is this the nature of the exhaust, a compromise of having loads ot torgue. Before i revert the exhaust back to the sip road 2.0 to check if the top speeds return, can anybody advise?
I know i am quibbling over 5mph top end speed and maybe i should just live with this but its irritating when i was getting higher speeds before. Any pointers you can give me will be most appreciated. Thanks.