Cavitation

[Bottom Bracket]

What would I be looking for? It’s a sporadic thing with the cavitation or slipping? The wood chunk was obvious when traveling 35, shook the whole boat.

Look for the other half of that stick or anything else that shouldn't be there.

 

[Patricko315]

By reading through all this, it sounds like your initial concern was solved when the piece of wood finally dislodged. It happened twice, not each time you throttled up. It doesn’t seem to me that the intake grate was a factor. It just sounds like you sucked up a stick and it dislodged and everything was good. That’s normal. You’ll get better at recognizing the sound and feel right away when it happens and there are techniques to dislodge it while on the water which you can read about in the forum. I find that I pick up stuff when I’m in wake mode or less because the boat is not pushing debris away. If I ever have to be in neutral, I just turn it off so not to suck something up then. I’m on the river with a lot of junk. When it happens again, to make sure it’s completely out, check out the pissers to see if they are both flowing good. Hope this helps.

Yes after removing the chunk of wood from the impeller all was good. Then on the next outing had cavatation on throttle up/slipped then good for the rest of the day. So either sucked something up or too hard on the throttles as others have suggested causing the cavitation. Definitely gonna address the poor sealant job on the intake area.

 

[FSH 210 Sport]

Yes after removing the chunk of wood from the impeller all was good. Then on the next outing had cavatation on throttle up/slipped then good for the rest of the day. So either sucked something up or too hard on the throttles as others have suggested causing the cavitation. Definitely gonna address the poor sealant job on the intake area.

Sounds like you sucked up something else to cause that cavitation.

 

[Patricko315]

Look for the other half of that stick or anything else that shouldn't be there.

It was a chunk of bark like a wood chip. I used a pair of pliers to get it out from the clean out port was wedged good. Luckily got it out was 10 miles from my Marina would have taken 2.5 hours to idle back. If it continues to do it will pull off the jet drive and inspect further. Pretty confident everything’s out.

 

[Patricko315]

From idle, just throttle up one engine to see which one has a problem. If it’s the port engine shut it off and put it in neutral, use the starboard engine in reverse to get going a bit, a few mph, then push the port throttle to wide open on the non running port engine. This will back flush the pump and remove debris that can be removed that way. Put the starboard throttle to neutral, place the port engine in neutral and Restart the port engine and test. I do this procedure first before opening the clean outs and it usually clears up what’s in there.

If you slam the throttles to wide open from a stand still you may get some cavitation even on a fully sealed up pump assembly. Not unlike the tires on your car breaking traction if you slam on the gas (got to get away before the jackers Jack) . If you roll into the throttles quickly you probably won’t get cavitation, if you do then think about sealing up all the nooks and crannies in the pump housing.

I like the spinning the tires analogy. I’ve been slamming the throttles wide open when taking off. I will try the rolling up slower method.

 

[Patricko315]

Also discovered missing a bolt on the intake grate when I crawled underneath. If it was loctited in no way it would fall out. Guessing just missed on assembly. Sloppy work. Called the dealer of course on back order no timeline for a shipping date

 

[FSH 210 Sport]

Also discovered missing a bolt on the intake grate when I crawled underneath. If it was loctited in no way it would fall out. Guessing just missed on assembly. Sloppy work. Called the dealer of course on back order no timeline for a shipping date

Pull one from the other side and get one from a hardware store.

 

[FSH 210 Sport]

I like the spinning the tires analogy. I’ve been slamming the throttles wide open when taking off. I will try the rolling up slower method.

Okay, then try just rolling into the throttles quickly and see if that takes away your cavitation issue. If it does then you’re done for the immediate future. Get some silicone and seal the clean out tray to reduce the amount of water that comes out of the bilge at the end of the day.

 

[sunbyrned]

Also discovered missing a bolt on the intake grate when I crawled underneath. If it was loctited in no way it would fall out. Guessing just missed on assembly. Sloppy work. Called the dealer of course on back order no timeline for a shipping date

Good catch!

 

[TeenGee]

Yes after removing the chunk of wood from the impeller all was good. Then on the next outing had cavatation on throttle up/slipped then good for the rest of the day. So either sucked something up or too hard on the throttles as others have suggested causing the cavitation. Definitely gonna address the poor sealant job on the intake area.

If your clean out ports fill with water, the first time you nail the throttles, the pump is sucking air causing cavitation. After running for a while with the ports filled with water, nailing the throttles might suck water but not air therefore no cavitation.

 

[Patricko315]

Pull one from the other side and get one from a hardware store.

Yep that’s the plan

 

[Patricko315]

I really appreciate all the helpful tips. Definitely a different animal than all the outboards I’ve owned. Other than these small issues overall very happy with the boat. I’ve owned several 4 stoke Yamaha snowmobiles and a F-300 outboard that were all bullet proof. Read great things about the 1.8 motors, so far these 1.9 motors have been great. Fuel efficient, quiet, quick acceleration, when not cavitating, and top end of 51mph so far. Seating layout is great for a 25 foot boat, 6 people aboard on one trip doesn’t feel crowded. Much more room then my 24ft Cobia center console.

 

[Patricko315]

Love the white with black hull

 

[Bottom Bracket]

Needs rod holders

 

[FSH 210 Sport]

Cavitation is usually caused by vacuum boiling of the water on impeller. This is sort of like when an airplane wing stalls, the air or water in this case breaks away from the impeller due to the vacuum being so high it causes the water to boil. Anyone who ever had a decent science class did this with a vacuum chamber and a dish of water.

If everything is sealed up, when you hammer the throttle at a standstill, the water on the intake side pulls away from the impeller blade and creates this high vacuum, the water boils the impeller starts to cavitate which reduces the mechanical force on the impeller and the motor spins the impeller faster exacerbating the vacuum boil and it spreads until it reaches an equilibrium. Once the flow picks up along with the boat moving this reduces the differential pressure between the impeller and the water, the boil starts to dissipate and the impeller starts to slow down as it is getting more force applied to it at the same time the water flow into the pump is increasing so the cavitation comes to end as all of these forces combine.

Whereas when you roll into the throttles the transition is slower and so is the differential force between the water and the impeller, lower vacuum, and the boat starts to move forward reducing the differential pressure even as more power is applied to the impeller.

If cavitation was caused by the tunnel not being sealed up properly, this cavitation would not go away while you were underway. Will sealing up the nooks and crannies help? Certainly can’t hurt.

The clean out plugs seal not being in good condition would allow air into the pump causing cavitation when that initial burst of power is applied and the pump would pull air down into the water creating a lot of bubbles which has the same effect as the vacuum boil and in effect causes the impeller to spool up and increase the differential pressure on the blades and vacuum boiling would in fact happen. So now at some point as the boat starts moving and the water flow increases and an equilibrium is reached and there is more pressure coming into the pump and water then starts to flow past the clean out plug bad seal and fills the tube with water thereby sealing the clean out tube.

Making sure the gap between the impeller and the wear ring is within spec is very important as is not having a dings in the impeller.

 

[Patricko315]

Cavitation is usually caused by vacuum boiling of the water on impeller. This is sort of like when an airplane wing stalls, the air or water in this case breaks away from the impeller due to the vacuum being so high it causes the water to boil. Anyone who ever had a decent science class did this with a vacuum chamber and a dish of water.

If everything is sealed up, when you hammer the throttle at a standstill, the water on the intake side pulls away from the impeller blade and creates this high vacuum, the water boils the impeller starts to cavitate which reduces the mechanical force on the impeller and the motor spins the impeller faster exacerbating the vacuum boil and it spreads until it reaches an equilibrium. Once the flow picks up along with the boat moving this reduces the differential pressure between the impeller and the water, the boil starts to dissipate and the impeller starts to slow down as it is getting more force applied to it at the same time the water flow into the pump is increasing so the cavitation comes to end as all of these forces combine.

Whereas when you roll into the throttles the transition is slower and so is the differential force between the water and the impeller, lower vacuum, and the boat starts to move forward reducing the differential pressure even as more power is applied to the impeller.

If cavitation was caused by the tunnel not being sealed up properly, this cavitation would not go away while you were underway. Will sealing up the nooks and crannies help? Certainly can’t hurt.

The clean out plugs seal not being in good condition would allow air into the pump causing cavitation when that initial burst of power is applied and the pump would pull air down into the water creating a lot of bubbles which has the same effect as the vacuum boil and in effect causes the impeller to spool up and increase the differential pressure on the blades and vacuum boiling would in fact happen. So now at some point as the boat starts moving and the water flow increases and an equilibrium is reached and there is more pressure coming into the pump and water then starts to flow past the clean out plug bad seal and fills the tube with water thereby sealing the clean out tube.

Making sure the gap between the impeller and the wear ring is within spec is very important as is not having a dings in the impeller.

Great explanation thanks!

 

[drewkaree]

Also discovered missing a bolt on the intake grate when I crawled underneath. If it was loctited in no way it would fall out. Guessing just missed on assembly. Sloppy work. Called the dealer of course on back order no timeline for a shipping date

A bolt. On backorder

They don't want to deal with this, and are hoping you just go to the hardware store and replace it yourself.

There's no magic metal in a Yamaha bolt, and the pitch and thread count are easy enough to figure out for even a shadetree mechanic, so I would consider that information you were told about back ordered bolts to be indicative of at least that person for that dealership, and perhaps next time try a different person for help - stuff like "backordered bolts" are a reason many here try to help when others have issues, and strongly encourage DIY when possible vs taking it to the backorder factory.

There's plenty to love about Yamaha's, and some dealerships that can leave you gobsmacked. We're here 24/7 if you need us, but we may also suffer from timely responses. The plus side is, we're often worth every penny we've been paid

 

[FSHER]

Also discovered missing a bolt on the intake grate when I crawled underneath. If it was loctited in no way it would fall out. Guessing just missed on assembly. Sloppy work. Called the dealer of course on back order no timeline for a shipping date

Sounds about right coming from a dealer. I'm frustrated for you, ha ha.

Does PN 90111-08833-00 sound right? I'm planning on taking things apart and resealing everything so I made a list of a few parts that I feel I could screw up and I might want to have on hand just in case. either way that PN seems to be available online through multiple vendors. 100% should be Loctited per my service manual.

The link below has helped me with parts identification.

2024 Yamaha AR250 (BXT1800AA) OEM Parts, Yamaha Sports Plaza

Shop our large selection of 2024 Yamaha AR250 (BXT1800AA) OEM Parts, original equipment manufacturer parts and more online or call at (503) 669-2000

www.yamahasportsplaza.com

Good Luck

-Mark