Definately worth a shot.
I had the exact same symptoms with my FZR1000 once.
I had switched the ignition,seat lock and tank lid after someone tried to pop my ignition with a screwdriver.....those Yamaha ignition tumblers are damn tough!!!!.......anyways,the gas cap I got was non-CA and thus was not vented in the same spot(no vapor recovery system).
I could get about 5 miles and then it would slowly die down to nothing.I could struggle home with the choke on and full throttle,since the big FZR has a fuel pump to kinda overcome the vacuum.I finally figured it out when I opened the cap and got a huge "Whoosh", from breaking the seal.