I recently purchased a boat with a 454 mpi with only 170 hrs on it.
I know little about the history on the boat. When you hit the throttle the response is slow whether it is sitting in neutral or in gear. Once the rpm's are up a little it roars to life and will fly, but the initial response is poor and should be much quicker. The only mods I know of are a set of wet headers.
If it were a carb I would be looking at the jets or for a vacuum leak. I am new to the port injection world, any thoughts? The motor purrs without a miss at any rpm, and response is great above 2000 rpm.

Injectors, ECM?

Thanks for any help.

Check the timing, i had a few where the distributor was a little loose and after time they would retard its self..

thanks, I'll check that out

Do the MPI's use a TPS that could possibly be causing the issue?

Yes and no ..if the tps were bad it would stall the engine when pulling the throttle back

I think it's over my head, I'll let the merc mechanic figure it out.