Odd performance issue

[BlackandTan]

Not sure I can really describe this but: Just got back from a 5 day lake trip, days 1-3 everything was fine. On day 4 I was using the cruise assist and had just decelerated to about 4000 RPM, and about every 5 seconds the engines would sound like they were straining for about a second and the bow of the boat would raise up a few feet, then back to normal, then 5 seconds later same thing. When the engine sounded like it was straining the RPMs remained steady. I continued on with the day having no issues until a little later it happened again while I was in no wake mode. I checked the impellers - all clear - and continued on. This happened a few more times over the weekend each time when cruise assist/no wake was engaged so I thought that that was my problem. Last day on the lake it happened again with no cruise assist. Anyone else experienced this?

 

[Julian]

Not heard this issue before...but step one I'd try on this sort of issue is to replace the spark plugs.

 

[Murf'n'surf]

Sounds like you are experiencing surging which usually points to you spark plugs needing a change.

You mean the bow was rising a few inches not feet, right?

 

[Ilmmct]

x2 on the plugs ... how's the oil level?

Interesting thread here if the oil is low:

https://jetboaters.net/threads/this-was-forwarded-to-me-anyone-ever-hear-of-this.7347/

 

[Scottintexas]

crazy stuff ???

the fact that your rpm's remain steady is puzzling,

did you check the cleanout grates or in front of the impellers, assuming not since you were on the water,

I wonder if maybe something isn't caught in the grate, maybe a plastic bag or something that while at speed is trailing or stuck to the hull but at no wake speed is being sucked up into the grate to cause cavitation, the surging and actual increase in thrust is raising the bow,

 

[BlackandTan]

x2 on the plugs ... how's the oil level?

Interesting thread here if the oil is low:

https://jetboaters.net/threads/this-was-forwarded-to-me-anyone-ever-hear-of-this.7347/

Funny you should ask. I regularly check the oil, and had just checked it that morning, and it was fine.

 

[BlackandTan]

I wonder if maybe something isn't caught in the grate, maybe a plastic bag or something that while at speed is trailing or stuck to the hull but at no wake speed is being sucked up into the grate to cause cavitation, the surging and actual increase in thrust is raising the bow,

That was my first thought. I should have tried the reverse and pull the lanyard maneuver. I did check the grates when I trailered the boat, they were clear.

 

[BlackandTan]

Going to replace the plugs this weekend. Thanks for the tips!

 

[BlackandTan]

Sounds like you are experiencing surging which usually points to you spark plugs needing a change.

You mean the bow was rising a few inches not feet, right?

I may have exaggerated a little, but the bow was rising at least 1 - 2 feet the first time. The lake was pretty rough at that point though.