piaggio zip 04 2t revs dying above half throttle

Hi,
I have a piaggio zip 50cc 2004 2 stroke. While it starts no problem, it suffers from power loss while revving over half throttle, the revs die until it finally cuts out unless you close the throttle.
Here are things I've checked so far:

Tank breather hose isn't blocked
vacuum fuel pump is working
Carb has been cleaned out with carb cleaner including jets and float chamber
all fuel hoses are clear of blockages
fresh fuel from Shell added

It even does it when up on the stand so I don't think its a roller or belt issue. I can't think what else it could be?. It was running fine with loads of power but now its a nightmare!

Any help appreciated

 

Thats the puzzling bit. I haven't done a thing to it, it was running fine and now its not. When you say flat ass rollers, what does that mean? should i replace the rollers?

I was going to put it into a Piaggio dealer to get it checked out by someone who knows them inside out, but he wanted £48 per hour

 

maybe your carb setup, the size of the jet maybe flooding it, or you could lower the rev's pin in the carb

 

Just a quick update to close this thread.

Found out what the problem was after much head scratching and stripping the bike down.

There was an air leak on the inlet manifold side which we tracked down to the reed valve not closing properly. Bought a new one and also replaced the inlet manifold as the rubber was a bit slack. total of £27 quid on Ebay. Scoot is back running sweet as a nut now