[GTSJK]

Replaced spark plugs, spark plug wires and rotor last year since it had been ~ 5 years since plug replacement and wires. Not sure if rotor every got replaced. Once I replaced them, I took the boat out right away and running up at WOT I now get ~ 300 rpm lower than I did before replacing. Used to get ~ 4400-4500 RPM, now only ~ 4100 ROM. I kept old wires and rotor, but not old plugs. Plugs are exact replacement for sure. I double checked to make sure that all wires were on firmly and in right firing order. What could be causing this? The Rotor was an OEM replacement (I think through Sierra). I am tempted to put the old rotor back on and see if I get the same results.
Any thoughts would be greatly appreciated!
This is a 1998 Z204 Jubilee (4.3L Alpha one).

[Hudson River Steve]

Quick thoughts, did you gap the plugs to OEM spec? Did you check the timing? Very slight tolerances in the rotor can affect timing slightly.

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[GTSJK]

No and No - two things I need to do.

[Hudson River Steve]

Originally Posted by Hudson River Steve

Quick thoughts, did you gap the plugs to OEM spec? Did you check the timing? Very slight tolerances in the rotor can affect timing slightly.

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[Scottie1961]

Ok, bear with me as I'm a car guy learning about marine engines. Does your engine have an ECM? If it were a car I'd say disconnect the battery and let everything reset. You may be getting different readings in sensors (do these motors have O2 sensors) which could affect how your ECM is advancing your timing. Or, it doesn't have an ECM and everything I just said is irrelevant