F150 issues

I have twin 150 four strokes and the port engine will not continually stay at any higher than 3500 rpms. The engine will rev higher, then decrease back to 3500. Everything is under warranty and yamaha claimed it was the fuel filter (which was replaced) but as of yesterday, the problem still exists. Just curious to see if anyone has had this problem and wanted to hear some of your possible explanantions. No ethanol has ever been used. Thanks.

[boats.net]

It could be a fuel problem but needs to be tested on water to find problem.

It was the fuel injectors.