New to me boat performance issues

[hardbound]

2004 palm beach 191 with a 2004 115HP 4 stroke Yamaha. Boat had seat for a couple years Dad just stopped using due to health issues. Pumped old fuel out of tank changed remote fuel filter fill tank with ethonal free gas. Started motor ran and sounded great . Loaded up two Saturday ago to go fishing myself and two buddys went to get on plane and boat struggled to do so. Moved more weight forward had no effect . Running 5200-5400 rpm only 20 mph. Spoke with Dad's old mechanic ask what prop was on boat I told him 19 he suggest that prop should be maybe a 16 . Found a 15 at locate prop shop to use. Put boat in water this past Saturday just my wife and I very light load in boat. Boat planed much quicker but at 5200-5400 rpm only 30 mph. I know this boat should not a speed demon but based on speaking with Dad he got much better performance than what I'm. Was planning on taking to dealer to have motor checked out this week. Does anyone have any ideas motor seems to running fine I'm at a lose not a mechanic?

[Tritontr19]

I agree engine is running fine with those rpm. I would suggest a stainless prop,
if still running the aluminum that comes with those boats. Perhaps a 17 to 18 p
for a test. Clay

[RSWORDS]

If the boat sat for two years and you didn't clean the VST, change the FP strainer, and get the injectors checked you are plying a dangerous game.

Get the motor 100%

[Gordon02]

Can you post up a few photos? Perhaps there is some set-up issues that we can spot. If the outboard is starting, idling, and running smoothly throughout the rpm range - then I don't join the engine problem camp. Your rpm numbers indicate the engine is performing.

I would like to see a photo from these perspectives -

1) Left/rear showing the boat and motor with the outboard trimmed down to where is was when you tried to get on plane.
2) The rear about propeller level so we can see the prop / hull bottom relationship.
3) Where the outboard was trimmed when it hit the highest speed.

It doesn't make sense that your Dad had good performance with the 19 and now it needs a 16. That's a huge change and unless it's a monster and heavy boat, a 115 should pull a 19" prop with ease. I'd like to see the photo of the "holeshot" trim you're using. Maybe the limit pin was moved up or there is some other reason you're not seeing the numbers you should be.

Gordon

[RSWORDS]

Low fuel pressure on an injected 4stroke will lean a cyl out on a motor that otherwise "seems to run fine". You need to check the VST. It may be beautiful or the screen may be half way plugged.

You already said it's down on RPM. (Should turn close to 6k) with the same set up as your dad. That sounds like classic clogged fuel strainer on the bottom of the fuel pump. Or a carb with issues if its carburetored

[RSWORDS]

The low fuel pressure pressure can make the motor seem normal but just down on top end power when the pump cant keep up with the volume needed because of the partially blocked strainer on the bottom of the pump.

You can Put a fuel preasure gauge on it and see if the pressure drops off, but I'd service the VST.

You went from a 19 to a 15 pitch prop and the max RPMs never changed.... think about it.... it's running out of fuel