Ive been told by a very reliable mechanic friend that a good way to get free top end horsepower out of an engine running dellortos (this might apply to webbers as well) is to drill out the filter in the end of the bolt which the fuel line feeds through. where the line enters the carb theres a built in filter which is a set of 3-4 holes which arnt big enough and starve the engine at high revs. drill them out and youll fix the problem.
vola!!

If the jetting & float bowl levels are set right you shoulndn't be running out of fuel up top, no need to do this.

i said something along the same lines but he said it still tended to starve and theres no harm in doing it, so its all good.

If we are talking about those porous brass fuel filters, they can (but don't usually) get clogged up. If they are partially clogged, I would just throw them out and use a standard line filter instead.