Fuel starvation..250hp 2 stroke

[Quinlivan]

250 hp 2 stroke yr 1999..read most post about fuel starvation ...new fuel pumps..ran on external gas tank...same problem after intial full throttle and planing engine will cut back to around 4000 rmps and slow its top speed... if i say below 4300 rmps engine runs fine..yamaha mechanic stated its a vapor separator ?? in the engine which need to be replaced...he pointed to a square metal box anterior to the fuel pumps ???... what is it and could it be just the carbuerators as several post indicate?

Thanks
Yamaha

[jb123]

does it indeed have a vapor tank? efi? or carbs as you mentioned. if so the FILter inside the vst may need to be cleaned.