97 mariner 225hp lost top end

Last few times I've been at the lake with a full tournament load and partner she won't get on plane until my partner sits close to the bow. Once on plane I'm only seeing 4600 rpm. WOT for my engine is 5800 rpm. Idle is low at 600 rpm. I've always used additives in my fuel and have upgraded my fuel lines. I did a compression test that came back with 105 on all six cylinders. Plugs are in great shape. The only thing I havnt checked are injectors but feel like it wouldn't run close to 4600 if it was something like that. Any and all advise is greatly appreciated.

may have dropped a cyl.
check all for fire at idle and make sure none of your plugs is fouled.

First check to see if throttle is going full throttle. Cables can cause problems. Which 225 do you have Model #. Some have a strainer on the fuel rail, some have a fuel pressure regulator, on and on.

Spro, We have seen these engines clog up the ex. tuner so bad that it restricts the exhaust from getting out of the motor thus grossly affecting performance. You can take the lower unit off and look up at the tuner with a flashlight and see if any of the holes are restricted. This may not be your problem but if all else fails look for this.

Good spark on all cylinders. ( plugs are wet but no carbon build up or damage will replace just in case after this test) Good fuel supply. (Replaced fuel filter today) compression good on all cylinders. I verified and adjusted the hot foot and I'm hitting full throttle on all stops. ( this my have been my issue because I was just a hair off from hitting full throttle. My serial number is OG519544. Year 1997 HP 225 mariner EFI. I will hopefully get out to test on Monday and will keep y'all posted. Thanks again for the input.

That ser:# no worky. Did the Sea Foam shock on a 2.5 EFI last week that all checked good but no power. Worked. Remove the spin on fuel filter, pour fuel into the fuel tank, fill with Sea Foam and re-install. Go to the lake.

Took a pic of the data plate and spark plug. Already filled the filter with sea foam.

Took the boat to the lake and sea foam blast did not work! Same exact symptoms. Replacing spark plugs and checking fuel pressure. It seems like she's starved for fuel on top end which leads me to think reeds or injectors.

Have you pulled sparkplug leads while motor is running? I would replace the manual fuel pump diaphragms just because I know with it being 1997 the diaphragms are hard. Normally when you have a lean condition you get a surging. Maybe getting time to check the exhaust tuner like Tommy suggested.

What would I be looking for by pulling the spark plug leads while the motor is running? Also dropping the lower is not a problem but how would I correct a clogged tuner. Thanks for all the help so far!!

To correct a stopped up tuner you have to pull the powerhead and exhaust system to gain access to the relief holes.

UPDATE.....replaced plugs and rebuilt mechanical fuel pump. Pulled all the plug wires separately and all cylinders dropped then raised rpm when the plug wire was reinstalled. Will test on the water tomorrow. If no results I plan on disassembling the VST and checking for debris. And last resort I will drop the lower and clean the tuner ports. Here's hoping. ...

Good Luck

Still no joy. Kevin ( roster) from temple marine outlet is bringing the computer to test for codes . Highly recommend him for any work y'all might have. Not only has he been available to answer I ton of questions he has gone above and beyond to help me out. I'll post tomorrow with what we find.