My 99 Waverunner has been running well since it's sbt engine install.. Plenty of power..

It will hesitate and stall when bike climbs to plane or if corning or leaning into turn..

My first thought was fuel, carbs have been rebuilt and filter replaced..

The fuel on/off valve is tight but it feels like it is turning all the way open.. I have noticed that when refueling a huge amount of pressure is released every time gas cap comes off.. I was thinking that the check valve on return side of lines may be sticking.. Anything else I should check..