Suzuki 225 4 stroke
 

My motor lately lost 400 RPM. It was running 5200 and and now only 4800. I had the filters changed last fall. It was running fine till about 6 weeks ago. Several times out the hole it would run 4000 and then I stopped the engine. I took off again and it did fine. It runs all day and never misses or skips. I had a spare prop that needed work so I took it and had it re pitched from a 23 to a 21. Put that prop on and still never gained any RPM. I had a compression check on it last year and then again 3 months ago. Everything good on compression. I was told by a friend that it may be another filter that they didnt change. I was wondering what yall think.

man I wished I could offer something.

If the compression is all good........ has to be something is the gear housing maybe??

Air filter?

I'm thinking it has to do with the computer.......sounds like its trying to save itself from something.....

Example. When its not getting oil it wont get over 500rpm.......if a sensor is missing something, the engine will adjust so it doesn't burn up....

Has your actual boat speed slowed down??? It could be as simple as the rpm gauge not reading correct.

Boat speed slowed about 4 mph also

Throttle linkage may have slipped on adjustment.......Had a Mercury that did that. Check the throttle box & linkage on motor

what do I look for?

is it a linkage?
my Zuke is all electronic.......no mechanical throttle.

I have to mention that on another site, it came down to the boat being waterlogged.

The throttle cable at the motor should attach to some type of linkage, there should be some type of adjustment there. Now whether or not you can tell if that adjusment has slipped or moved, wouldn't know without looking at it. "If" it has moved you may be able to tell where it originally was set.

Fuel or ECM problem
 

This is something with your fuel delivery or your computer.

I doubt it's your linkage. Even in the case that it did slip, once you changed to a smaller pitch prop it should have picked up RPMs.

Do you have a fuel/water seperator? If so, check around the top edge for any rust or small holes. Also, check your primer bulb for any cracking where you can lose suction in your fuel line.

If you can't find anything in your fuel delivery, it's your computer. If it's telling your injectors to pump harder and run richer, or anything of that nature, that may be why you're losing RPMs.