Yamaha SX190 how fast

[ScottS]

Definitely cavitation burns on the face of your impeller. How is the gap between the leading edge of your impeller and the wear ring/side of the tunnel? Is it consistent? I think it should be something like .023” to .03” (Anyone feel free to correct me) which should be tight and consistent all the way around. If it looks like there is spalling on the leading edges, an inconsistent gap between the impeller and the side, and/or damage to the wear ring/sidewall, these will all affect your performance.

Confirm that you installed the correct spark plugs as well - NGK LFR6A (SX195 uses NGK LFR7A) at a gap of 0.8-0.9 mm or 0.031-0.035 in

 

[Gidder10]

Well crap. So now what? Just replace impeller or more?

 

[ScottS]

Well crap. So now what? Just replace impeller or more?

You may not need to replace the impeller yet. If the gap between the leading edge of the blades and the side of the tunnel isn't too bad then this may not be your primary issue. You will have reduced performance, but I suspect you have other issues.

Where are you boating? are you at high elevation? Are the water and air temperature very high? These will both effect max RPM.

When you are boating, is there water coming out of the side of the boat from what is affectionately called the "pisser" and is it very hot? This can point to a heat sink issue that some address by upgrading the intercooler on the boat to the SX/AR195 intercooler ($600 or so). Heat sinking the engine causes the engine management system to throttle performance. Although I have never heard of it causing anyone as much performance loss as you describe.

For example, I boat around 4000-6000' above sea level. As air temps have gotten into the high 90's and water temps into the mid 70's I saw my RPM drop from about 7400 down to only 6200. I put an elevation adjusted impeller on and regained most of those RPMs.

Replacing your impeller is not too expensive - you can do it yourself if you have a vice, a 1 1/8" wrench, and the muscle. If your wear-ring is damaged, that can be a bit more pricey - I think I saw someone have a dealer quote them 975 for both recently - that was to rebuild the pump (which includes the impeller and wear-ring to my understanding).

Let us know what you see around the impeller as far as how big the gap appears and if it is consistent. Pictures always help.

I would also confirm the other engine bay related items laid out by myself and others as a double-check.

Out of curiosity, how many hours are on your engine? Do you boat in sandy or gravel heavy areas? Do you beach your boat often? These can all help people diagnose possible issues.

 

[Theryan]

The impeller doesn't look damaged except for the discoloration or burn as others have said. The wear ring doesn't look overly worn, either. Is your impeller an aftermarket one or OEM?

Have you checked your intake grate under your boat? Completely free of any blockage?

As someone else said check to see if your "pisser" is flowing properly and if it seems overly hot.

Throw some stabil in your fuel to address any issue you might have from moisture in your gas tank.

If you lose power when turning like you said it could be an issue with your fuel delivery, as well, like a fuel filter for instance. Or your spark plugs could be fouled up.

 

[tdonoughue]

So I second (or third, fourth?) the cavitation burn. But yours does not seem at a consistent distance from the edge of the impeller (which will happen if the issue is at the impeller edge). And, that looks clean too.

I would be getting a caulk gun, taking off the intake grate, and caulking everything leading up to the impeller. I zoomed in on some of the photos and I think I see a lot of gaps there. And with a '15 that is about when mine went. It likely needs recaulking with some silicone caulk in every gap. Where the grate meets the hull, where the hex nuts hold the grate to the hull, etc. Everywhere that ain't smooth should be.

I bet you will have a world of difference.