Here's the situation: Last year my boat ran 4700 rpm and 62 mph...The boat was winterized at a marine shop that doesnt see many performance boats (first time Ive gone there) and stored on a trailer in a covered storage unit during the winter.

This spring I can only seem to get 4400 rpm and 58 mph out of her. The boat runs like a top but Im struggling to get on plane if fully loaded (no issues getting on plane with 4 or less people) and I have this rpm/top speed issue.
Does anyone have any suggestions as to what could have happened during the offseason or what I should be checking....

I'd check the simple stuff first. Hows the plugs and wires? Are all connected properly? Curious, carbed or FI engine.



Darrell.

How old is the fuel you are running? Did you have the same amount of people and gear on board as last year, Or do you have more now? Check your prop to see if it was damaged or bent while in storage, Look close some SS blades can be bent but hard to see some times And if all that is ok then you might want to start with a tune up and full service. And while they are in there you might want to do a comp test & A Leak down test to be safe.

The engine is a 1994 454 magnum efi. The plugs and wires were replaced 1 year ago and the boat ran all last summer at 4700 rpm and 62 mph.

Ive been boating now 5 times this year so the fuel is new (Chevron gas) and Ive been running 87 octane. Ill check the prop a little closer and see if I missed something.
I didnt think I would need a tune up because I only went boating about 5 times last year after it was tuned up but maybe I should have the plugs and timing checked (although the boat purrs like a kitten once on plane).
Ill have the compression checked too but how can I lose compression with the boat just sitting on the trailer?

Hard to say, It is just guess work with out being there looking it over, Also [FYI] inside the VST fuel tank mounted on the engine you have a fuel pump inside that tank, And a lot of times the filter at the end of the fuel pump will get dirty and could lower the fuel pressure some or make the engine down on power, Have your fuel pressure checked also.

YUP,

I would check fuel filters.

this might not be relevant but a different idea. I had a scarab that had twins. one of the motorsa wouldn't come up to full rpm as the other would. my problem turned out to be the rpm gauge was steeling the electrical current from the motor. all ran great except for not reaching full rpm. my .02 good luck