yzf 750

Hi folks,its my first yamaha and i see potential.... ive bought a yzf 750 . It seems when i take her out first thing she runs sweet but then she backfires and doesnt give as much power as she could ,somthimes it feels like the power is kind of cutting back in. Anyway i removed the airbox and noticed that there was black from the backfire going into the airbox. i then removed the plug from that cylinder and it looked fine. i did take the bowl of the base of one of the carbs not the forth one because it was too difficult but there was what llked like rust deposits in there. i did run it low on fuel and it had been lying up for a while. sSoO............i plan to buy a long allan key to remove the carbs and clean them.

Hey any input would be great and thanks for your time.

Aidan

p.s im just back on a bike after a 12 year and a stroller....lol