df 175 lmited to 3500 rpm intermittently

[racjah]

My twin 2013 df 175 came on the boat which is new to me. shipped from Georgia to me in Maine.
the problem happens intermittently going along with both tacks at 4500 rpm. when the port side motor cuts back to 3500 and stays there. so i match the tacks again.. then I look back again at the tacks 5 min. later the port motor is back at 4500 ..
it seems to be that the lower rpm is more often than the high meaning that the fuel system it is staying clogged or something? more often than not.. but when you least expect it the flow comes back ..for a short time.. like when i hit a wave..
the engine does seem to sound more bogged i can hear some difference when cruising. it does get to plane and goes fine no sputtering or any codes on the dash. but when i push the throttle up to get more there is no difference in the motor sound just stays at 3500 rpm. while the other throttle will go to 6ooo + rpm if i would dare to run like that.. but i don't..
so i have changed all 6 filters 3 on each motor.. 2 on the engine and the fuel water separator.. also had my wife pump the ball in the fuel line when running at 3500 rpm to see if that would change the problem.. no change/
next i plan to check the high pressure fuel pump/screen/lines? any other ides would be great.. or could it be blocked air flow? thanks

[Harper]

You might be barking up the wrong tree. There's a neutral detection switch on the throttle lever holder of the engine. It's operated by the clutch control lever to prevent starting in gear. Once the engine is running, it will also limit the RPM to approx 3500. Since it is a simple on-off switch (on in neutral, and off in gear), I think it possible that the adjustment is just barely in the position where you can start, but be so close to being "on", that it might on occasion slip back to the "on" position, causing the ECM to sense that you're in neutral, thus limiting the RPM. You mention that it sometimes comes back to the correct RPM after being physically jolted ("like when i hit a wave") which would also indicate to me that it might be right on that edge of being out of adjustment, or might even be loose.

[racjah]

Thanks Mike if it ever stops raining here i will check that first.. thanks again for the reply