RPM fluctuation at low speed - twin F150

[RobD1220]

Good Morning,
Last week, I was out cruising the ICW as I haven't been out in a month or so due to weather, work, etc. On my way back to the ramp I noticed my port motor (I have twin Yamaha 2012 F150 4 strokes with approx. 590 hrs.) rpm's started to fluctuate without any movement of the throttle. The rpm's were at 1300 then dropped to btw 1000-1100, then down to 700-800 to then back up to 1300. I started to get worried so I gave the engine gas/throttle and it held fine at 1500 and 1700 rpms. This happened a few times on the way back until I reached the ramp (but noticed it was only at that current RPM of 1200-1300). At the ramp, when putting the boat on the trailer and just in gear there were no issues. I have asked several friends, other Yamaha owners, etc. and have heard things such as the primer ball, fuel water separator or the TPS. I haven't had a chance to look into yet but will soon. I was wondering if anyone has experienced this issue and/or has any idea to what it may be.

[JerEazy2]

take off your fuel water separators, dump them out (pour the gas into your truck or lawnmower) refill them with clean gas and a splash of seafoam or ring-free, put them back on (better yet replace them - and fill the new ones with clean gas they aren't expensive). If that solves the problem then you may have some watery fuel.

If it doesn't, we can dive deeper.

[RobD1220]

take off your fuel water separators, dump them out (pour the gas into your truck or lawnmower) refill them with clean gas and a splash of seafoam or ring-free, put them back on (better yet replace them - and fill the new ones with clean gas they aren't expensive). If that solves the problem then you may have some watery fuel.

If it doesn't, we can dive deeper.

I will give that a try - appreciated the response.

[TownsendsFJR1300]

You should have an engine fuel / water separator under the hood. It faces forward. Yank the hood inspect (and or dump)..

The clear cup (more yellowish):

That red ring, if there's water inside, will float.

I believe your newer engine has a sensor (and wires) in that cup that detects water.

[RobD1220]

You should have an engine fuel / water separator under the hood. It faces forward. Yank the hood inspect (and or dump)..

The clear cup (more yellowish):

That red ring, if there's water inside, will float.

I believe your newer engine has a sensor (and wires) in that cup that detects water.

Question: would an alarm have gone off? I am going to take a look at this as soon as I get home. thanks for your response

[fairdeal]

Question: would an alarm have gone off?

when present and working correctly, water in that filter, tripping the water-in-fuel switch, causes the keyswitch warning horn to sound - but only when in neutral.