2015 Yamaha SVHO - Power loss

[rstier]

Hi,
My 2015 Yamaha SVHO is experiencing a loss of power. Typically I can hit 70 MPH but max speed now is about 38-ish with the max RPMs at 5500. It only has 98 hours and I recently replaced the plugs, did a oil/filter change and fresh fuel. Still no luck. It starts and runs fine, just the loss of power. I also checked the impeller to ensure nothing was caught in there. Also no errors on the display and it seems to be pumping water fine. Any thoughts on next steps for troubleshooting?
Thanks!

[seabrook]

start it and listen for the sc noise (rattling sound) also check for boost leak by removing the seat and bliping the throttle with your face close to the intercooler

[Green Hulk]

Hi,
My 2015 Yamaha SVHO is experiencing a loss of power. Typically I can hit 70 MPH but max speed now is about 38-ish with the max RPMs at 5500. It only has 98 hours and I recently replaced the plugs, did a oil/filter change and fresh fuel. Still no luck. It starts and runs fine, just the loss of power. I also checked the impeller to ensure nothing was caught in there. Also no errors on the display and it seems to be pumping water fine. Any thoughts on next steps for troubleshooting?
Thanks!

Either your supercharger clutch needs to be replaced, or you have a boost leak. To verify your supercharger clutch take the inlet off of it and try to spin the supercharger impeller both ways. If it spins both ways it's toast and needs to be replaced. This is the clutch kit you need
Yamaha 27-Sprag OEM Supercharger Clutch Kit - Gasket and Chain Guide Bolts Included [2013neweryamclutchkit] : PWC Performance Parts (4-tecperformance.com)

If your clutch is fine, then check for a boost leak where the hose from the intercooler connects to the throttle body. More info here
Where/how to check Yamaha SVHO J-Tube (J-Pipe) at Throttle body - Greenhulk Personal Watercraft Performance Forums

[K447]

Either your supercharger clutch needs to be replaced, or you have a boost leak. To verify your supercharger clutch take the inlet off of it and try to spin the supercharger impeller both ways. If it spins both ways it's toast and needs to be replaced. This is the clutch kit you need
Yamaha 27-Sprag OEM Supercharger Clutch Kit - Gasket and Chain Guide Bolts Included [2013neweryamclutchkit] : PWC Performance Parts (4-tecperformance.com)

If your clutch is fine, then check for a boost leak where the hose from the intercooler connects to the throttle body. More info here
Where/how to check Yamaha SVHO J-Tube (J-Pipe) at Throttle body - Greenhulk Personal Watercraft Performance Forums

I will suggest checking the J-tube first, as it is more definitive. If the hose is not properly in place, you can tell without removing anything.

Well, you may need to remove the plastic engine cover. Then look down where the rubber tube connects to the throttle body.

[skeeterzx225]

I had this same thing happen to my 2015 SVHO, its likely the J tube, another way to easily tell is to take the rear seat & storage bin off and see if you have exhaust exiting when throttle is added...once that is fixed make sure your timing chain is upgraded or you have a ticking engine bomb...

[K447]

I had this same thing happen to my 2015 SVHO, its likely the J tube, another way to easily tell is to take the rear seat & storage bin off and see if you have water misting everywhere when throttle is added...

Why would there be water misting from the J-tube?

[skeeterzx225]

Why would there be water misting from the J-tube?

yeah, bad choice of words...I meant exhaust...I just remember when test riding without the rear seat there being some very fine mist floating around in the engine bay when I rev'd, likely due to any residual condensation inside...

[rstier]

Hi all,
Thanks for taking the time to reply, it’s been very helpful. I checked the clutch and it only spins in one direction. So that seems to be ok. The pipe that connects to the air box was a little loose, so I tightened that. I was excited thinking that was it but after tightening good and taking for a test ride, still no luck. I did find the small outlet tube that presses into the pipe near the top of the engine was loose. I see it just presses into the tube but I noticed some type of sealant residue around the fitting. I’m wondering if that needs to be sealed tight? If so, any idea on the type of sealant to use? I attached a pic so you can see what I mean. I did find the J-Pipe and that appears to be tight on both sides. Still troubleshooting.
Thanks,
Ron

[K447]

... I checked the clutch and it only spins in one direction.
So that seems to be …

Unfortunately that test can only tell you if the clutch has failed entirely. A sprag clutch that slips under load can feel just fine when checked using finger pressure on a non-running engine. A slipping Yamaha clutch will be unable to deliver proper boost when running on the water at speed.

The only places a boost leak can occur are between the supercharger and the intercooler, and between the intercooler and the throttle body (the J-tube). Everywhere else in the intake system contains non-pressurized air so a ‘leak’ there would not affect engine power in a substantial manner.

Did you check inside the J-tube for signs of water?
If the intercooler has developed a water leak into the air side then the engine will be ingesting water when riding at speed. At low RPM the water pressure is less so the engine can run seemingly normally while at higher power levels the water ingestion reduces the available engine power. The engine may also run ‘weird’ if it is drinking enough water while generating power.

[rstier]

Unfortunately that test can only tell you if the clutch has failed entirely. A sprag clutch that slips under load can feel just fine when checked using finger pressure on a non-running engine. A slipping Yamaha clutch will be unable to deliver proper boost when running on the water at speed.

The only places a boost leak can occur are between the supercharger and the intercooler, and between the intercooler and the throttle body (the J-tube). Everywhere else in the intake system contains non-pressurized air so a ‘leak’ there would not affect engine power in a substantial manner.

Did you check inside the J-tube for signs of water?
If the intercooler has developed a water leak into the air side then the engine will be ingesting water when riding at speed. At low RPM the water pressure is less so the engine can run seemingly normally while at higher power levels the water ingestion reduces the available engine power. The engine may also run ‘weird’ if it is drinking enough water while generating power.

Good to know about the clutch, thanks. I did not pull the j-tube off to check for water. Being at the bottom of the engine, it was fairly difficult to get at. I reached down and pulled the J-tube on both sides and tried to move the clamps with my hand, both which seemed pretty secure. Is it possible I may have sucked in weeds or other debris into the intake and it’s just not visible? Since it seems to be pumping water OK, I wouldn’t think so. I did double-check to see that low RPM mode was turned off with the remote control. Not sure if that is something that ever malfunctions. I’ve never run it with that feature turned on but the way it is running right now is how I would expect it to perform if that feature was enabled.

[K447]

Review the basics;

Does it rev to redline out of the water?

Check cylinder compression.

Inspect spark plugs. Does any one of them look different from the others?

What spark plugs are installed?

If you engage Low Power mode while on the water (shut off engine to switch), does it run any differently?

Jet pump clogs generally do not restrict engine RPM. Often the engine revs higher than normal when full power is applied.

[rstier]

Review the basics;

Does it rev to redline out of the water?

Check cylinder compression.

Inspect spark plugs. Does any one of them look different from the others?

What spark plugs are installed?

If you engage Low Power mode while on the water (shut off engine to switch), does it run any differently?

Jet pump clogs generally do not restrict engine RPM. Often the engine revs higher than normal when full power is applied.

Hi, the ski is at my camp and I won't be back until next weekend to troubleshoot further. Before I left, I checked the plugs and they all looked the same/good. They only have a few hours on them since I just did the maintenance. The model on those is NGK LFR7A. One thing to note is I had the same issue with the previous plugs. I didn't notice if it redlines when I rev it out of water. I will check that on Saturday. I will also test Low Power mode to see if there is a difference. My compression gauge was at home, so I will check each cylinder as well to see where compression is at.
Thanks!

[HardRider]

You describe perfectly what happened to two of my Ski's with bad plugs. I would replace the plugs again, maybe you have a bad one, wrong gap, I assume you used what originally came with it. My Ski's ran perfect just no power.

[skeeterzx225]

first check for the pulled away hose, then swap the plugs if the problem persists...When I had my issue I swapped the plugs first, turned out it was the dislodged hose issue, old plugs were fine..

[rstier]

You describe perfectly what happened to two of my Ski's with bad plugs. I would replace the plugs again, maybe you have a bad one, wrong gap, I assume you used what originally came with it. My Ski's ran perfect just no power.

Thanks for the tip. I have some plugs I kept as spares from the season before when all was good. I can swap with those and double-check the gap as part of the process of elimination.