Cyl 1&5 Not firing

2002 Four Winns Funship w/Volvo 270Gxi. Idles well, will not perform under load. OK until trying to accelerate when the boat struggles to get on plane, RPMs hard to come by.
We have determined #1 and #7 not firing. All injectors rebuilt and put back in; new cap, rotor and plugs. Swapped plugs and injectors with cylinder we know is good, nothing changes, but the injectors work well in a new location.
Took fuel rail assembly out this morning cleaned it with Gumout, blowing compressed air through the large hose, and replaced. Small hose would not allow air through it, should it work like larger hose? Still an issue, will not go on plane.

Anyone with ideas? 6 of 8 run fine, 2 do not!

Re: Cyl 1&5 Not firing

Did you do a compression test?

Re: Cyl 1&5 Not firing

2002 Four Winns Funship w/Volvo 270Gxi.

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What is the full model number of your engine, or the serial number, no such thing as a 270GXi.

Re: Cyl 1&5 Not firing

sqbtr said:

Did you do a compression test?

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No.

Re: Cyl 1&5 Not firing

Don S said:

What is the full model number of your engine, or the serial number, no such thing as a 270GXi.

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I would have to check the identifiers, but it is a 270HP Volvo Penta 5.0Gxi

Re: Cyl 1&5 Not firing

Plug wires on the right plugs? How old are the spark plugs? Wires ok? cap and rotor ok? Getting fuel to those 2 cylinders?