G'day. Sounds very much like you have blockages in the carburettors- probably the main jets & emulsion tubes.
You will need to remove the carburettors, diss-assemble them & thoroughly clean them.
I thought that this link may help if you want to do it yourself.
It will show exploded diagrams of them.
http://www.mrcycles.com/fiche_section_detail.asp?section=281601&category=motorcycles&make=YAMAHA&year=2002&fveh=6827Particular attention to parts-8,9,10,11,& 12.
I feel sure you'll find part 11(main nozzle) will have blockages in the pin size holes in the side of it.
These are critical for proper fuel atomization. They commonly get blocked by a goup that forms in the carbies when fuel has been left in them for a long time.
I jope this has been of some help
Regards Andrew Porrelli