Yamaha SX190 how fast

[Gidder10]

How fast should I be able to go with 4 adults (800-800lbs) on board a cooler and a monster tower? 2015 Yamaha SX190.

 

[Theryan]

My guess is around 40 mph (speedo - haven't GPS tested). With just a couple of people and calm water I can get mine to 50 speedo, but with a more full boat it tends to be around the 40. Could maybe push it to 45, but the water is never that calm where I feel safe doing so.

 

[Gidder10]

So mine does 15mph. What the heck is wrong? I changed the spark plugs and reseated to back plug. You have just one engine right?

 

[Theryan]

I do, yeah. My guess is that you have cavitation going on.

 

[Gunner]

40

 

[Brad460]

You guys always leave out details...ok it only goes 15 mph...What RPM is the engine turning? When did this start? Was it a gradual decrease?

Mph is a result of other factors, not a cause..

 

[jeffrt]

Mine will do right on 40 with 4 people on board. No tower.

 

[Dwrat]

Check your prop for debris.
40 mph easily.

 

[Gidder10]

You guys always leave out details...ok it only goes 15 mph...What RPM is the engine turning? When did this start? Was it a gradual decrease?

Mph is a result of other factors, not a cause..

Between 6-7 thousand rpm, full throttle. The next morning, when cold it got up to 30 mph For about one minute then started dropping with in one min back to 15 mph. I limped into the dock and dropped off the two guys and then with just me and another girl it did 30 mph and did not drop. But that was the top speed I Could get it to.

 

[OrangeTJ]

There is clearly a cavitation issue or your reverse bucket is impeding the flow coming out of your pump.

 

[Dwrat]

Is it idling smooth?
Could have bad new plugs????
My guess is the impellor has something stuck to a blade like a small chunk of wood.

 

[Gidder10]

There is clearly a cavitation issue or your reverse bucket is impeding the flow coming out of your pump.

It’s not the bucket. I checked that. So how do I fix a cavitation issue?

 

[Theryan]

It’s not the bucket. I checked that. So how do I fix a cavitation issue?

Pull the service plug and put your hand down in there to feel around and see if there's anything stuck on the impeller, if there feels like there's any damage to the impeller, etc. Feel around the wear ring to see if there's anything seeming out of place or wrong with that.

Go behind the boat with a good flashlight and with the bucket all the way forward look into the jet pump from the back and see what you find regarding the above (any damage, stuff stuck, etc.).

If there's damage you'll have to pull the impeller (it's really easy, honestly) and replace it.

The other thing to check and see is to make sure that your service plug is actually seated 100% correctly in the port. When I first got my boat, the guy that I bought it from never took the plug out and when I took it out (as you should after you're out of the water) it would never fully seat even though I thought it did, and it never let me get above like 5-10 mph. That would be my starting point here, honestly. Make sure that it's fully in there and not just wedged. You need the back pressure that that plug creates, otherwise it's massive cavitation.

Take pictures of the impeller from the back and whatnot if you can and post them on here and we can take a look.

 

[Gidder10]

What do you think?

 

[Theryan]

Are you able to get a flashlight or flash on the photo to see the impeller from the back there?

The other option is to take your phone and hold it carefully as you put it down into the clean out port and take a photo with the flash facing the impeller, but you'll probably want to take several just to make sure that it focuses correctly. We can't really see much from those photos currently, unfortunately.

I'm trying to make out what I'm seeing on the wear ring and whatnot, but it just isn't bright enough.

For the clean out port plug, when you insert it and lock it in place, does it stay locked in place, or can you pull it out or move it at all (without pressing the button to unlock it)?

 

[ScottS]

Cannot really see anything from the pictures. Use a flashlight and look into the back of the jet/pump for signs of any debris. Also, you can crawl under your boat and look up through the intake grate and see if you any issues.

You can also open up the engine compartment and open the air filter box to make sure there is nothing in there that is restricting airflow.

I would also pull the plastic cowling/cover off the engine and make sure that the spark plug ignition pack/coil on each spark plug is fully seated on the plug. Also, make sure that each plug is fully seated in each ignition pack.

If you want to go deep enough, you can pull each spark plug and replace them - ensuring that you have proper gap - check the manual for proper specs.

You also should try to get a good photo of your impeller (prop) so that we can see what condition it is in. There will be pitting and erosion if your boat is having an issue with cavitation - meaning when you go to wide-open throttle (WOT) your RPMs jump and bounce at the rev limiter around 8200 RPM. This photo will also allow us to see the tolerance between the leading edge of the impeller blade and the wear ring to see if you have an issue there that is reducing pump efficiency.

 

[biffdotorg]

You showed everything but the intake. Cavitation starts at the intake. If it is full of grass/weeds, wood etc, then it will cavitate, as you cannot pull any water through.

Show us your intake grate and what it is full of. As 10mph at 6000 rpm is just that, cavitation.

 

[Gidder10]

Are you able to get a flashlight or flash on the photo to see the impeller from the back there?

The other option is to take your phone and hold it carefully as you put it down into the clean out port and take a photo with the flash facing the impeller, but you'll probably want to take several just to make sure that it focuses correctly. We can't really see much from those photos currently, unfortunately.

I'm trying to make out what I'm seeing on the wear ring and whatnot, but it just isn't bright enough.

For the clean out port plug, when you insert it and lock it in place, does it stay locked in place, or can you pull it out or move it at all (without pressing the button to unlock it)?

It will go maybe 25 or 30, then once I turn or stop and start again I lose all power and even after I plain out again it only will go 12-15 mph with four adults. It’s like the engine isn’t getting what it needs. Like if it were overheating. But it’s not over heating.

 

[Gidder10]

The plug seats tight

 

[biffdotorg]

I'm no expert, but that's cavitation burn on your impeller. It's got to be out of spec. It should be even colored from edge to edge, and yours shows burn.

If you have 6000 RPM and minimal boat movement, you are not hooking up. It won't go to 6000 if the engine is not running right. Heck I was rolling 6000 RPM with two engines last night, and only doing 10mph, but I was also hauling 1600lbs of ballast!