Another Cavitation/Loss of Top Speed Thread...

[AboveTheBest]

I’m on my 3rd season with the 242 and the top speed has gone down since I picked it up, but has settled around 45. When I picked it up (used) it was getting up to 51.

My RPMs still get up to 7500 on both sides but the speed isn’t there anymore.

I remember someone mentioned that repeatedly going WOT from a stop has an affect on our boats in this regard, and that is a maneuver we do about 6 times every outing as my family is made up of slalom water skiers.

I plan to pull the pumps next time I’m out of the water and give a good once over with 4200, as maybe cavitation is my issue.

My question is; will my WOT from a stop continue to get me down this road? If so I may not worry too much about the “issue”, as 45mph is still plenty fast for us and I don’t want to fight something that will continue happening every month....

 

[Babin Farms]

How is the bottom of your hull? Have you waxed the entire hull(mainly the bottom)? How much more gear do you have in your boat than when you initially were gong 50mph? Any amount of weight will slow the boat down. I seen 49 for my top speed after we bought ours and haven't seen it since, been close but that was before we loaded it with extra cabin speakers, tower speakers, wire to run speakers, mirror, Garmin, cable , transducer, extra life jackets, grill, propane tanks, tool kit, power inverter, blower, tubes, ski's, wakeboard racks, assortment of kids toys, VHF radio, fenders, ropes, tote with cooking supplies, sunscreen, head, second anchor and whatever else I can't think of. Every little thing adds up when it comes to weight & that will scrub speed. Most don't even think about how much they put in their boat because it's usually just a few things at a time.

 

[AboveTheBest]

How is the bottom of your hull? Have you waxed the entire hull(mainly the bottom)? How much more gear do you have in your boat than when you initially were gong 50mph? Any amount of weight will slow the boat down. I seen 49 for my top speed after we bought ours and haven't seen it since, been close but that was before we loaded it with extra cabin speakers, tower speakers, wire to run speakers, mirror, Garmin, cable , transducer, extra life jackets, grill, propane tanks, tool kit, power inverter, blower, tubes, ski's, wakeboard racks, assortment of kids toys, VHF radio, fenders, ropes, tote with cooking supplies, sunscreen, head, second anchor and whatever else I can't think of. Every little thing adds up when it comes to weight & that will scrub speed. Most don't even think about how much they put in their boat because it's usually just a few things at a time.

The first year of the power loss I thought it might be due to build up on the hull from leaving it wet-slipped all year, so I acid washed it and the next time out there was no increase in speed. This year I spent a 20+ hours stripping the gel-coat down and buffing/polishing the entire boat (it looks amazing BTW), and still no help to the speed.

As to weight, there is no increase in stuff, people, or gas that is affecting the top speed. It will do the same speed with just me and a quarter tank of gas, and the lake I boat on always looks like glass. Good point though on the weight.

 

[2kwik4u]

Don't check jsut weight increase, check weight placement as well. Without trim to adjust the boat attitude on plane, we can't compensate for wonky loading. I think the 19ft'ers are more susceptible to this than the 24ft'ers, but it's still a thing to watch for.

Check oil fill in the engines, overfill can cause a slight drop (50-100rpm) in engine revs. As can old/bad grease in bearings. Might be the additive culprits that dropped you from 7,700rpm to 7,500 rpm. Our pumps are non-linear in flow, so a few hundred rpm could be the difference between 51mph and 47mph.

I would suspect that at some level you are also getting some wear on the impeller and wear ring. As that tolerance between the impeller and ring open up, you might be losing small amount of pump efficiency leading to a drop in a MPH or two a year.

To directly answer the question. Aside from the nominal wear mentioned above, I seriously doubt "hammering down" from a dead stop is having any effect on top speed.

 

[Babin Farms]

Maybe the impellers or the wear rings are getting wore. If your waters are anything like ours over here it's like putting liquid sandpaper through the pump

 

[AboveTheBest]

Thanks for the help. I’ll take a look and may end up replacing the wear rings this year anyway with the plastic/replaceable liner style.

 

[Scottintexas]

I've never heard of the WOT from start causing loss of top end and I don't understand it,

were they trying to say the immediate increase in RPM causes cavitation/wear on the impellers ???

my guess would also be you probably have some wear in the impeller leading edges or a gap in the impeller/wear ring



.

 

[AboveTheBest]

I've never heard of the WOT from start causing loss of top end and I don't understand it,

were they trying to say the immediate increase in RPM causes cavitation/wear on the impellers ???

my guess would also be you probably have some wear in the impeller leading edges or a gap in the impeller/wear ring


.

I’ve been searching for the thread where it was mentioned, but I believe you’re correct that they said it caused wear on the impellers... it made sense when I read it, but now I can’t find it.

I think the post said that over time that could happen.

 

[Scottintexas]

one thing I love about Yamaha boats is that we have jetski's to compare as to how they can handle the "abuse" factor,

think of how many skis and how many times people go zero to WOT, a multiple factor I probably can't fathom ( I know a little girl who does it consistently on @Betik ski) and we don't hear about them losing a lot of top end,

does it cause some deterioration over time, I wouldn't doubt it, I'd look at other possibilities first,



.

 

[Betik]

My ski’s throttle position has one two settings. No wake and WOT.
Compression readings from last year were more consistent on the ski (MR 1) vs my 1.8HO on the boat. Ski has about 107 hours and the boat about 115ish.

 

[Betik]

I’m on my 3rd season with the 242 and the top speed has gone down since I picked it up, but has settled around 45. When I picked it up (used) it was getting up to 51.

My RPMs still get up to 7500 on both sides but the speed isn’t there anymore.

I remember someone mentioned that repeatedly going WOT from a stop has an affect on our boats in this regard, and that is a maneuver we do about 6 times every outing as my family is made up of slalom water skiers.

I plan to pull the pumps next time I’m out of the water and give a good once over with 4200, as maybe cavitation is my issue.

My question is; will my WOT from a stop continue to get me down this road? If so I may not worry too much about the “issue”, as 45mph is still plenty fast for us and I don’t want to fight something that will continue happening every month....

I can all but guarantee this is not a WOT issue and I can explain the reasoning ……

I purchased our 2012 sx240 in October of 2016 27 hours on both engines. In May of 2017 and while preparing for Bimini I did go to WOT at the lake and with a full tank of fuel + 320lbs of human flesh we got to 52mph as per the Garmin echomap.
Between then and October of 2020 our boat has seen WOT maybe 2 or 3 times and all occasions i have noticed 44mph to maybe 46mph. in late 2019 I noticed port engine maxing at 7,000rpm and the boat not being able to plan on the port engine alone sbtd engine could plan the boat. I attributed to an impeller because in July of 2019 Ingested some crap. We don’t tow or use the boat for much so I never really bothered to open the pump.
during winterization in October of 2020 I noticed an oil like substance in front of the port engine. Long story short I realized that I screwed up during winterization and the port air filterblue protectant we use for winterization. I ordered new filter from Yamaha and still waiting for them to arrive. I will test drive at end of June and see if that will solve my WOT at 7,000 rpm.
So to return to you original question we rarely WOT on the boat and we have seen a reduction on top speed. and if I had to bed I would say that you a similar or other issue than WOT.
BTW, since we got the boat we have put 100 hours , added trip tabs, added sound insulation, caused some mystery damage on the throttle assembly and the our hull is as clean as it gets for a 10 year old boat.



hope this helps

 

[AboveTheBest]

A little follow up on this as I know this topic gets searched often…

I replaced both wear rings with the plastic liner style units and also gave the impellers some attention while I had them off. One of them had a small ding in it that I was able to correct and file back into place.

I also sealed the intake tunnel with marine silicone while I had it all apart.

I cleaned and waxed the entire boat, and the first run with all of this done and I saw increased hole-shot/torque while pulling a skier (likely the impeller fix) and an increase of about 1mph on the GPS.

By the end of the year this had dropped down from 45 and 7500 to 43 and 7350.

I’m wondering if I’ve been adding too much oil during my oil changes (I use the full 4 quarts), or if my air cleaners are getting nasty.

The boat is coming out of the water for the season this weekend and I will see what I can find out during my end of the year maintenance/storage prep.

 

[Cobra Jet Steering LLC]

Well always measure the amount of oil you remove and replace that exact amount plus the oil filter amount, You should occasionally check your oil with the boat in the water just so you know it is not low or overfilled.
After an oil change when first on the water check the oil level and carefully add any extra to get the oil on the dipstick between the two marks at the top, I also carry a large plastic baster syringe with a plastic tube and a empty oil can to remove any excess oil if I somehow overfilled it . You may just need new spark plugs though Also take care about your oil filters they can rust and leak or if they are really thin walled they can split either way it is a bad day on the water if it happens, after my experience I changed to Fram tough guard 3600. https://jetboaters.net/threads/new-oil-filter-failed-just-did-the-oil-change-2-weeks-ago.18678/
If you are loosing both r p m's and top speed it isn't going to be cavitation, because with that r p m's go up - speed goes down.
Also check all exhaust clamps for leaks , as they are known to fall off due to rust and any exhaust in the engine compartment will cut the top end speed, probably not the case but worth checking.

 

[proplessdancer]

Has anyone simply tried replacing the spark plugs? i am on year 4 with an AR195 and first time out this year it was chugging at WOT. called a couple people much smarter than i and said to replace them regardless of how they looked. all 4 appeared fine but replaced as instructed and problem fixed

 

[Julian]

A little follow up on this as I know this topic gets searched often…

I replaced both wear rings with the plastic liner style units and also gave the impellers some attention while I had them off. One of them had a small ding in it that I was able to correct and file back into place.

I also sealed the intake tunnel with marine silicone while I had it all apart.

I cleaned and waxed the entire boat, and the first run with all of this done and I saw increased hole-shot/torque while pulling a skier (likely the impeller fix) and an increase of about 1mph on the GPS.

By the end of the year this had dropped down from 45 and 7500 to 43 and 7350.

I’m wondering if I’ve been adding too much oil during my oil changes (I use the full 4 quarts), or if my air cleaners are getting nasty.

The boat is coming out of the water for the season this weekend and I will see what I can find out during my end of the year maintenance/storage prep.

What is the gap on your wear rings? (I'd have to look up the tolerance).

One way to check the air filters quickly is to just do a run with them out.

 

[AboveTheBest]

Has anyone simply tried replacing the spark plugs? i am on year 4 with an AR195 and first time out this year it was chugging at WOT. called a couple people much smarter than i and said to replace them regardless of how they looked. all 4 appeared fine but replaced as instructed and problem fixed

I think many (including me) change the plugs yearly.

What is the gap on your wear rings? (I'd have to look up the tolerance).

One way to check the air filters quickly is to just do a run with them out.

I’m not sure on the tolerance, but to be honest the old wear rings looked just fine after I pulled them…

I’ll pull the filters and see if that improves performance on the last ride this weekend.

 

[Julian]

I’m not sure on the tolerance, but to be honest the old wear rings looked just fine after I pulled them…

It isn't just the wear ring, but the impeller too.

These are the tollerances from my 2005 SX 230 Service Manual.....(probably not much difference model to model)

 

[Tgen2013]

The variables that can affect your speed most likely are:
1. ignition
2. Fueling

I can't speak for your model but after my first two seasons I changed my plugs from the oem CR's to the NGK iridiums. I immediately saw higher speeds, and greater fuel economy even with the higher speeds.
The tuning of my FRT motors loves this combo.
I also changed from using 87 no ethanol to 91 no ethanol. 10 years later I have the same top speed, and even when wake surfing all day I don't use more than 15 gallons of fuel.

Your impellers are not going to deteriorate that much to affect your top speed unless you put some rocks or cables through it.
So think about it. I weigh down my boat with 1200 lbs of water. Then from a stop repeatedly drive her to 7300 rpm and hold her there. For the last 10 years,............LOL.

Here is what I use for impeller bearing lubricant.

Cerma STM-3 Hi Temp Lithium Grease

Cerma STM-3 Grease is the best lubrication grease sold anywhere! Cerma STM-3 Grease reduces maintenance, extends lubricating intervals, increases equipment life, reduces operating temperatures, and extends bearing life.

www.cermastore.com

And NO water doesn't do shit to this. I use it for my washout plugs too. This stuff is the best heat/anti-seize. Been using it for a decade.
Agree,.............. changing plugs are the easiest way to keep these boats humming.

 

[2kwik4u]

It isn't just the wear ring, but the impeller too.

These are the tollerances from my 2005 SX 230 Service Manual.....(probably not much difference model to model)
View attachment 165632

I'm always amazed at those clearances. Human hair is about .004in. So the range is LITERALLY 3-5 hairs, with a max of 6.......in an assembly that is mass produced, comprises of multiple materials from different production processes, and has to process all manner of debris/dirt/etc.

Quite astounding really.

 

[Julian]

.3mm a grain of salt....