Modern Vespa

As I noted elsewhere I recently had Gabriella serviced at 20000km. As part of that I asked them to fit my 2nd hand Akrapovic exhaust. At 10000km we fiddled with the rollers to try to flatten the acceleration and appeared to improve things. With the new exhaust the shop felt it needed more help and we have lighter weights to try to hold it in a "lower gear". Initially the scooter seemed quick off the mark, but if the throttle is wound open to beat the traffic across an intersection I'm first across the white line but the acceleration from then on is disappointing - I described it to them as being as flat as a turd 💩.
We are trying to figure out if the exhaust is causing the problem, or the weights being too light, or something different like the clutch taking up too quickly and too well. It was in amazing condition when we looked at it, what wear there is is very even, but minimal.
So, has anyone got experience with adding an Akrapovic HP to a 300GTS [2017)? If so, what are we missing?

Ever heard of Back pressure, it might bee worth a read. Also swap the exhaust back and leave the weights to see if it changes.

I always find they are better left standard.
Vespa spends millions designing them

My guess, wrong roller weights. Doubt it's an exhaust issue. But I'm just guessing

It isn't a question of "wrong" weights, the issue is that the intake/displacement/exhaust/weights/variator shape/clutch spring/transmission gears are an interrelated system. These components were selected together by Piaggio, but you modified first the roller weights (to your liking) and now the exhaust and the roller weights again (not so much to your liking). The shop took a guess on the second roller weight change and you don't like the result. So change them some more! It's a trial and error process unless you have a dynamometer. If you're running out of acceleration too soon, I think the rollers need to be lighter.

Thanks for the input. In jest I suggested they put it on their non existent dynamometer. They are keen to work to get it at least how it was so we will continue. Their thought is that we are being thwarted a little by a fuel map designed to comply with Euro regulations and we are dancing around it trying to overcome the dead spot created. The option of going back to original remains.