High RPM Very Little Thrust

[Erikbmlny]

I have a 2017 Yamaha 190FSH Sport. I recently went out on Lake Erie and only could get it up to 20 mph under full throttle. (I have had this boat since April and feel I've never gotten the speed out of it that says it should go. Full throttle 1 person 34 MPH.) And while I was out boat RPM's went very high and lost almost all thrust. I first pulled clean-out plug and couldn't really find anything. So limped back to port at about 3000 rpm maybe 2mph. If I gave it throttle rpm's went up with a lot of rumbling.
I then pulled from the water, trailer ed it home, and proceeded to take the back apart removing the impeller and shaft. I was expecting to have damaged impeller but it looks fine. I did find a small piece of stick, less the diameter of my little finger wedged crosswise. Is that enough to lose almost all thrust? I did have a little thrust, barely enough to get back. Would love to get feedback on this problem. Thanks Erik

 

[Cobra Jet Steering LLC]

that is the culprit you can be sure of it. high r p m no speed is called cavitation even a small bit of fishing line or a piece of plastic will do the same thing as will weeds one place to be careful is at the boat ramp backing off the trailer, reverse kicks up trash into the pump.

 

[Erikbmlny]

Thanks for the lightning fast reply. And I’m happy to hear it’s as simple as that. I love the boat but it’s a little bit of a dog. Any thoughts on increasing speed or thrust? The additional weight I would have is a trolling motor on front port and two batteries for that centered in changing area. I go about 34 mph by myself and 28 with one additional person. Or is that just the speed parameter of this boat? By the way I will looking at the Cobra Jet Steering products at the end of this season at next pullout. I appreciate your input.

 

[Cobra Jet Steering LLC]

The speed certainly does sound a bit low, I would be looking at the spark plugs first, and the throttle to insure it is opening the throttle body to full throttle.
And be sure there is not any exhaust leak in the boat having carbon monoxide in the hull will slow the heck out of the engine from lack of oxygen. So check hoses and clamps . Just a few things that come to mind.

 

[Erikbmlny]

Thanks again for your help. I’ll check out all of those things.

 

[Cobra Jet Steering LLC]

ok, hope it helps.

 

[Pro Build]

Thanks for the lightning fast reply. And I’m happy to hear it’s as simple as that. I love the boat but it’s a little bit of a dog. Any thoughts on increasing speed or thrust? The additional weight I would have is a trolling motor on front port and two batteries for that centered in changing area. I go about 34 mph by myself and 28 with one additional person. Or is that just the speed parameter of this boat? By the way I will looking at the Cobra Jet Steering products at the end of this season at next pullout. I appreciate your input.

How high of rpm's do you normally get at full throttle?

 

[Erikbmlny]

Excellent question. I haven’t paid attention to that at all. When I put back in the water next week, I’ll write down all the rpms at different speeds. I normally just cruised at no wake speed until I reach the lake and just open it up without even looking at the rpms. But I will now. And then I’ll answer back. Thanks again.

 

[Liftr]

This little twig caused the same symptoms for me.

 

[Cobra Jet Steering LLC]

That is big actually just something as small as a water bottle cap can cause serious cavitation if it gets hung up in between the impeller blades.

 

[Speedling]

That is big actually just something as small as a water bottle cap can cause serious cavitation if it gets hung up in between the impeller blades.

True enough!
And some lakes will have an influx of debris with spring rains lifting stuff from the shores.
Lake Cumberland has gotten me bad in the spring with debris, needing to dig for wood chips like much size getting wedged over and over. Sometimes the marina will look like it has a floor or chopped up wood across it until it gets stirred up and floats down stream. Haven't figured if fast or slow is the way to go in that garbage.

 

[Erikbmlny]

That is about the size of the stick I had. It’s good to know it’s that simple. Albeit a pain. I did pull the plug and did not feel the stick to be able to pull it out. At least I know for next time. Thanks for showing me.