2001 SCR 2900 trouble getting on plane

[ScubaDave16]

I have a 2001 SCR 2900. I purchased in Oct 2022. It has a single 7.4 mercruiser with MPI injection and Bravo 3 drive. It has always been underpowered since i had it, but this season it has been having a lot of trouble getting on plane. I leave the stern drive all the way down since i keep it in a marina slip. It has hydraulic levelers as well. This season even at wide open throttle and the levelers down it takes several minutes to get on plane. if there are 4 people in the boat forget it. it gets to 4300 rpm, but thats it. I don't have a lot of stuff in the boat and usually only keep the water tank partially full and the waste tank is pumped out. The engine oil, filters, and fuel filters have been changed this season.

I do notice a somewhat loud hissing noise from the engine at certain RPM. almost sounds like a vacuum leak, but is there even a vacuum on this motor?

any ideas on what if anything I can do? Thanks in advance.

[mmwjr]

First I would verify that the bottom and drive are free of marine growth. Yes all engines create vacuum as the piston travels down its bore. While you are achieving neat WOT I would still perform a compression and leak down test to verify health.

[ScubaDave16]

Thanks for the reply. the bottom is clear of marine growth. I have done compression tests on small motors, but have no way to do a leak down test. i'm assuming if those fail that means new engine or rebuild. since its the busiest boating month of the year, Im not sure I want to start anything that would mean major repairs especially since i have no place to work on the boat (and no one local I know who would repair it at the dock).

[mmwjr]

Have you removed the spark plugs to see how they look? Do you know when the engine was last tuned up?

[Mr Hemi]

4300 RPM is too low.
If it cant reach Max 4600RPM, you might be under propped.

There is several prop shops that have a calculator to figure out prop slip based on RPM and speed.

Going from a 3x3 on my Bravo 3 to a Solace 4x3 and dropping down a couple pitches completely changed how boat got to plane and time needed.
Now i dont even need to use my trim tabs to get on plane.

Before you start tackling the motor figure out your prop.
I would guess dropping from say a 26P to 24or even 23pitch would get you in to 4600 RPm range and a 4x3 will give you better bite to get up on plane with.

Even if you drop your pitch a bit to far, the only thing you will loose is top speed, which most dont use.
hissing noise is normal as far as I am concerned.
My 2 cents./\