Single Engine Loss of Power @ 4500 RPM - New Boater 2006 Yamaha AR210

[Jeff G]

Hi everyone, i am new to the forum, this is my first post, first boat and I am doing my best to get it back to perfect working order.

The latest issue is that one of the engines has power loss after reaching 4-5K RPMs. It is intermittent and if I were in a car it sounds as though the throttle isn’t dropping into gear. I took a video but I'm not sure how i can post it. I have RPMs but the engine is running at a higher pitch and I have no power. After a few minutes running the engine geared down, my best description, and was working perfectly for a 15 ride. Then, on the way back to the dock, the engine again didn’t have top end power.

I have already changed the spark plugs on both engines and pulled, took apart and cleaned the clean-out plugs, using a car jack, since they were stuck. But I found nothing in the screw when I reached down to clean out any blockage or debris.

Any help or suggestions would be great. I am hoping it is something I can fix on my own.

 

[Murf'n'surf]

Sounds like cavitation. You'll need to pull the cleanout plugs and feel around for debris in the impeller. Or put it on the trailer and go under the boat with a flashlight. You migh have a small piece of debris wedged in between the impeller and housing.

Other possibilities:
Damaged impeller
Loose or missing caulking around the pump intake and tunnel

 

[itsdgm]

Welcome @Jeff G and sorry to hear about your issue. I agree with @Murf'n'surf your problem sounds like cavitation. If the power is there until mid range rpm, then the rpm's spike and you're losing power. It's caused by air getting into the pump. The air gets in there from turbulence caused by either a dinged impeller, missing sealant on the pump or pump inlet, or by debris in the pump (something as small as a toothpick or piece of fishing line). So look again really close, maybe it's in there.

 

[Zonie]

Ditto. You might consider pulling the pump on that side. It's a very easy process and there are several good youtube videos out there. If you discover it's caulking, do them both at the same time.

 

[Scottintexas]

@Jeff G glad to have you on board, you've also have a couple of members in your area who might could help you trouble shoot it,

I agree with everyone else that it's probably some sort of cavitation

while your trouble shoot,
1. confirm what your RPM's are on each engine
2. can you nurse it slowly to act right
3. definitely look at it on the trailer
4. check both the impeller but also the intake grate and in the tunnel that they have good silicone, see if you can pull the silicone along the edges with your fingers,
5. the fact that your cleanout plugs were frozen in place tells me the previous owner didn't do much maintenance, be careful with the #3 spark plug, it can get seized

you have to post videos to youtube or another place and then you can add the link to your post,
Pictures you can copy and paste directly in your post,

 

[Jeff G]

.Thank you everyone. I plan to pull the pump and check the seals next. The plugs are back in and secure but I plan to get two rebuild kits. I put it back in the water after checking the plug, reinstalling it and checking the tunnel. I didn't find any sticks or weeds. After running for half the day perfectly it then decided to start acting up again. I was running the boat near a shallow fresh water sandbar though and I suspect that maybe it could be sand/dirt? Not sure if that would do it. Also, when it initially went weak, I still ran both engines, one cavitating, but i kept the RPMs matched on both and it dropped back into full power after a few minutes. I wanted to share the pic below of how I was able to remove the plugs since I know many people have difficulty. It took some serious pressure. I will also work on posting the cavitation video.

 

[Jeff G]

Everyone, i took all your advise and took out the impeller and checked the seals.

The impeller looks fine and there was no debris in the tunnel. It looks as though there was missing silicone around the intake but could that really be the cause? I am not sure where to add sealant. One engine runs fine and the cavitating engine will go up to around 4000 rpms before "gearing down" with the same rpms but without the power. I can nurse it up to almost 7000 rpms but it eventually kicks down. I did notice that when i make a sharp turn the engine goes back to full power for a brief moment. And the water jet coming from the side of the boat, the cooling outflow (please forgive my terminology), is half as powerful and barely coming out, vs the other engines outflow, when the engine starts the cavitaion.

Does anyone know someone in the Charlotte NC area that would be able to take a look or assist? Any recommendations?

 

[Scottintexas]

This is a post about my missing sealant and cavitation with pictures,
https://jetboaters.net/threads/cavitation-missing-sealant-in-pump-grate.884/

 

[itsdgm]

Yes. That missing sealant can/will cause turbulence in the pump causing a loss of thrust. The cooling water comes from the pressure/output side of the pump. That's why you're losing cooling water flow when the pump cavitates. The fact that it's better while turning one direction is because water is being loaded or "packed" into that pump more while turning.

 

[Beachbummer]

If you need to use the boat before you can fix it, you might be able to feather the throttle slowly to prevent cavitation. As you accelerate slowly you give the pump a chance to fill with water without sucking as hard, and you may be able to accelerate past the issue without cavitation.

The issue is probably easier to reproduce by stomping on the throttle. The rapid demand for water will likely exacerbate the problem.

 

[EAnguiano]

I have a similar issue with the same boat and before I start taking stuff apart I want to ask if the engine light ever came on? As mine did and also has a loss of power..