Modern Vespa

Icannot accelerate more 30km/h I've checked the front suspension the brake fluid is intact no air in it,the parking break too is OK what could be the problem

I had this problem when I picked up my Piaggio 150 Fly from the mechanic a couple of weeks ago. It wouldn't go over 45kmph. I took it back in and they found they had put a spring in wrong in the carb somewhere. Have you done any work on it lately and something might have come loose?

First suspect would be a fuel supply issue.

Start with the basics by installing a new fuel filter and a fresh load of fuel from a quality source.