Much higher fuel burn on 2 out of 3 engines - what can I check?

[rdiesel01]

0t81917 -0t819125 - 0t819123
This Forum has been such a help in getting me to understand Optimaxe's Thanks to Don, Savage and many others - Thank You. So now my latest question is in regards to fuel burn. Last year I had the Starboard powerhead replaced with a Mercury Factory reman. The port and centr engines are burning 15-16 gph vs the starboards 8 gph @ 4000 RPM's. Is there anything that would cause such a difference in fuel burn?? Anything should be checking? Thanks

[EuropeanAM]

Same prop/pitch on each, same throttle setting, and same RPM's? Unless there is a mechanical problem (note: engine wear can play a factor), one of these items is likely not the same.

[MetalliStratos]

That engine cannot be seeing the same load as the others. I don't know how the engines are synced....is it rpm based, throttle position or?
Could that engine be running in aerated water so it sees less load?

[rdiesel01]

Just repropped the engines 21p Rev 4's on the outside engines 23p Rev 4 on center - this is the way the boat was propped from the factory.Went from Bravo 1's to the rev 4's. RPM's set exactly the same - 4000