May be the fuel vent line or tipover valve is getting plugged. Several folks have had the vent line get water in it and stop the venting, which then stops the flow of gas to the carbs. Quick temporary fix is to loosen or remove the gas cap.
After the cap is removed, you can also see a vertical hollow metal tube sticking up about an inch or more. This is the fuel vent line, and a hose connects to the bottom of it under the tank and that proceeds to the fuel tipover shutoff valve. Below that is another tube leading below the bike.
If you cut that bottom tube at approximately a 45 degree angle at the bottom of it, then the rain water cannot plug the vent tube.
You can check the system by blowing into the metal pipe under the gas cap using a separate spare length of tubing). It should blow thru easily, if not then it was plugged, and just blow harder to unplug the vent line/tipover valve.
There have been previous posts about this somewhere.
