Strange goings on in the fuel department...

[unfazed]

First things I would check is aiir filter to see if it is dirty or the intake is partially blocked.
Check the fuel filter, do you know when air filter and fuel filter were last changed?
Is the air vent in the tank clear?
Is the fuel line kinked?
Check these first as all are easy to check.

:agree :lol Check the easy things first, before you go assuming things.

A common problem is fellows routing the fuel pipe over the frame brace instead of under it and the tank flattens the pipe limiting the fuel flow.
And as flakey says it could be a blocked vent and opening the fuel cap will solve it
Put some white paper sheet under the carbs and open the drain screws to see what crap comes out. The remnants of water petrol mix can be a gelatinous substance (if the bike has been out in the rain and idle for a while) which can clog the main jets.