yamaha 225 4 stroke outboard running rough

[oceanvibes]

I have a yamaha 225, 4-stroke outboard that had been worked on by a mechanic as the heads were clogged up, there were major internal corrosion issues and the end result being, having to replace one cylinder head. From the time the new cylinder head was installed the engine starts fine but runs as if its missing on one of the cylinders and sneezes/backfires when trying to get on a plane, backfire happens between 1500 and 3000 rpms, above 3000 it runs fine. Tests indicate good fire and compression on all cylinders, all sensors, oil, spark plugs, filters etc have been changed and engine still runs rough and backfires as indicated above. Can anyone help please??

[boats.net]

Did they get camshaft belt timed properly, do they have plug wires on right cylinder, do they have throttle bodies sync. properly?

[oceanvibes]

Yamaha 4 stroke outboard running rough

the timing seems right to me when I checked unless I'm missing something, the two marks on the cam shaft pulleys line up perfectly when the flywheel line up mark is on TDC. All spark plug wires are in proper positions, I have seen them crossed before so I know exactly what that sounds like. The only thing I'm not sure about is the throttle bodies synced, never heard about that one before. I had sort of a similar problem with another engine and when I checked, the compression was low on one cylinder and when I pulled it off realized that the mechanic had installed a head that had valves that were pitted, and not seating, however the engine in question does have good compression on all cylinders

[rodbolt17]

compression test on an F motor is equivalent to teats on a boar hog.
run a leak down test.