I have a Vespa GTS300 and have sometimes problems with the fueling of the bike, it feels like the fueling is not in a constant flow. The dealer has clean and replaced many of the parts that could be the problem but that didn't fixed anything...
If anybody knows anything about this problem please tell me
I guess you have an earlier model of the Vespa GTS300, earlier models of the Vespa GTS300 had a problem that the regulator/rectifier had a bit of a low voltage on the electrical system, also the cooling of the regulator/rectifier was not adequate enough and therefore in hot conditions (read Thailand) it could generate problems that best are described as uneven fuel injection operation.
If your Vespa GTS300 is still with warranty you should point this out to the dealer, if you not have any warranty you can still try to get into contact with Vespa Thailand or Vespa HQ in Italy... as an alternative many aftermarket parts manufacturers currently sell plug-n-play replacement regulators/rectifiers. Normally a new regulator/rectifier cost for the Vespa GTS300 about 4500 THB.