225 4stroke backfireing

[crayman]

I have 2 2003 225 4 stoke yamaha`s one is coughing sputering at 1500 rpm when i pump the bulb its ok up t 4000rpm then wont go any harder other motor runs 5400 rpm,motors have just had 200hour service, i checked main onboard filer clean cant find any leaks up to motors , will lift boatout of water and check under cowl, will check all conections ect, any clues if not sucking air what the prob may be
Maurie

u need to check fuel pump,fuel lines and vent lines
if the bulb goes flat, u have a air leak