Losing Thrust @ 5000 RPM’s

[Vedner19]

I own a 2009 Yamaha 212SS. I took it out today and both motors seem to cavitate at around 5000 RPM’s. Motors sound strong and operate as they should below 5000 RPM’s. It’s responding the same as when there are weeds in the impeller. Both impellers are clear from weeds or anything else. Any ideas? I tried attaching a 10 sec video but getting message that file is too large. ?

 

[84rzv500r]

clearance between the impeller and the housing?

condition of the impellers?

condition of the stator veins?

nothing not even fishing line wrapped around the shaft?

Pump tunnel to hull sealant condition ?

Mid bearing seal condition ?

how munch load in the boat ?

 

[Vedner19]

Thanks for the response!

I plan on taking the pumps off tomorrow to inspect the impeller housing and the impellers. I’ll inspect the other things you mentioned as well. Not much load, my wife and I.

 

[Cobra Jet Steering LLC]

I would be looking for an internal exhaust leak I had a similar situation once and it was a beast to figure out try clamping the hatch switch and leave it open a few inches and see if the issue goes away also look for water in the hull from a loose exhaust hose it will usually happen around the mufflers if one is filling the engine compartment with carbon monoxide both will be starving for oxygen and as we all know the clamps used usually rust and fall off
One more possibility on the older engines check the air cleaners , if someone did an oil change to both engines and they overfilled the oil , it will clog the filters and choke the engine at speed , for both to do it is possible if the same person did them both at the same time and overfilled them , the excess oil goes straight to the filter from the breather tube, on newer engines they placed the breather tube after the are filter so the excess oil goes in to the cylinders and gets burned off.

 

[Vedner19]

I took the nozzles off the pumps and inspected the impeller housing and impellers. The impellers are new and the impeller housing liners were also new. Could it be the threaded housing that the impeller shaft slides into is stripped? Or could it be sucking air from where the pumps mount to the stern causing cavitation?

 

[FSH 210 Sport]

Was it working right before or did you just buy the boat?

 

[Vedner19]

Was it working right before or did you just buy the boat?

Just bought the boat

 

[FSH 210 Sport]

I took the nozzles off the pumps and inspected the impeller housing and impellers. The impellers are new and the impeller housing liners were also new. Could it be the threaded housing that the impeller shaft slides into is stripped? Or could it be sucking air from where the pumps mount to the stern causing cavitation?

If the shafts were stripped they wouldn’t work at all.

As @84rzv500r asked, what is the clearance between the impeller and the wear ring? It shouldn’t be more than the thickness of a credit card. I recently set up a pair of impellers and set the gap at .014” as that is the minimum clearance.

You say that it acts as though it’s cavitating at 5000 rpm’s. What does it do at higher rpm’s or WOT?

What is your top speed?

If I had to venture a guess this problem is happening just before the boat gets on plane and the nose is high?

 

[Nightmare]

I know that Florida has no mountains, but did you take the boat to altitude over 5000 feet?

 

[Cobra Jet Steering LLC]

I just thought of one other reason this can cause this to happen, IF you have stale fuel in the tank, since you just purchased it I would suggest adding some high test to it and see if that fixes the issue. or improves the situation

 

[Vedner19]

Impellers are new. Impeller housing liners are new. I’ll inspect the shaft teeth tonight.
Gas is good. I’m in Florida as far as elevation goes.

I wish I could post this video I have of the issue. Is there a way to post a video on here?

Do we have information anywhere that shows the proper way to seal the jet pumps?

 

[Nightmare]

Post the video to Youtube and link it

 

[Vedner19]

Good idea, here is is:

- YouTube

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

youtube.com

 

[FSH 210 Sport]

Are your clean out plugs seated?

Do you get any speed out of it at all?

 

[84rzv500r]

if the cleanout plugs are in it are the reverse gates open? that sounds like its in neutral... and I saw 7000 on the tach so the engines are functioning normally

will it move in reverse?

 

[Vedner19]

Yes, clean out plugs are in and reverse gates are good. The boat starts to accelerate like it’s trying to get on plane. Everything is good until it gets to around 5000 RPMs and then it’s like the impellers are slipping, forward momentum stops and the RPMs jump from 5k to 8k RPMs. You can see it in the video.

 

[84rzv500r]

did you leave your anchor down? ?... sorry but its happened to lots of people and might be another badge

its unlikely that both sides would have issues in the tunnel...

when idling in neutral tied up to the dock do you see any little bubbles coming out of the jet drives?

If the impellers and wear rings are new this is where you need to start.. and I suspect something is grossly wrong as my experience is that even with junk and outta spec and broken parts the jets will still move the boat if the impellers will turn

this is gonna get complicated now because your gonna have to move to the next level of detail... can you check the impeller to wear ring clearance with feeler gauges for each blade at the trailing, middle and leading edge and then rotate the impellers 90 degrees and measure again....

if this is in spec which i am beginning to doubt... I'm leaning toward a mismatch in parts wrong overall diameter for the impellers or a 160mm wear ring on a 155mm impeller...

 

[Cobra Jet Steering LLC]

contact the dealer where the boat has been serviced and ask them what was wrong with it on it's last visit they will probably tell you hoping you will bring it in for it to be fixed .

 

[lazergeek]

Anything abnormal on the hull or intake grate that would disrupt water flow into the tunnel? What about the seal around the clean-out plugs?

 

[Vedner19]

So I took it out on the water this morning and tried a few things. Issue seems to be more on port side and definitely a cavitation issue. I tried starting at WOT and it got through the cavitation at around 8,000 RPMs and then ran perfect topping out around 56 mph. I stopped and started this same way several times and it would do the same thing each time. You could feel the cavitation around 5,000 RPMs but then would get past that point and it would feel as if the impeller caught and had full power.

I came home a took off the pumps. Lots of corrosion and missing sealant in several areas. Lots of corrosion on intake grates as well. I sanded these areas down. Based on the pics I attached could this be causing the problem? Impeller and impeller housing clearance is within spec.

I’m assuming I should seal up these cracks and crevices with some RTV and attempt to make the tunnel as smooth as possible?

I’ve also seen some info on a pump shoe seal/stuffer. Could the pump shoe cavity be causing the cavitation?

Everyone’s help greatly appreciated! ✌??