Yes I know another Cavitation Issue. I have tried everything I know. HELP!

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Please forgive me if I am not posting this in the correct section. I have seen Cavitation threads on here and some are closed and I have done the two fixes but still experiencing problems. I am new but have seen and used much of the advice here and am very grateful.
Here is what I own:
• 1997 SeaDoo Sporster single engine Rotax 85hp motor.
• Bought used a month ago so I could give to son.
• Starts and runs but the gas is old and still has the separate oil tank.
• I was going to empty fuel but it is topped off and I have no way of getting rid of that much gas so I put a gasoline stabilizer in the fuel.
Week one:
• Took the boat to local lake and she fired up but rpm is high then settles down after a minute.
• Left the dock where through the no wake zone. When I brought the throttle up it just reeved the motor with very little forward movement.
• Took it back and order a wear ring, brand new stainless impeller, shaft bearings and seals. (Thanks for the freezer trick for the wear ring it worked great.
• Wear ring was bad a lot of clearance. Impeller had some dings in it, oil was stinking and less than half full. Shaft was OK but I wanted to replace everything including the needle bearings and seals.
• Slapped it all back together.
Week Two:
• Same lake put boat in and started up just to notice water gussing in around the boot.
• Took it back out and went on the forums and I ordered a complete shaft rebuilt kit less the shaft since the shaft splines were fine and shaft appeared true.
• Ordered new parts and replace accordion boot all three O rings, carbonite, and carrier bearing (believe what they are called and the front boot.
• My carbon piece was scarred badly and the boot was hard on both ends.
Week three:
• Same lake put boat in started right up no leaks. Did notice the carrier bearing moving about a 1/16 inch in a vibrating motion.
• When I went to use full throttle at this time it almost got on plane before what felt like it was flooding. I believe if I had not backed down on throttle it would have died.
• Back to the dock called a good friend of mine up north that works on outboards and he said sounded like a carburation issue and I should have them rebuilt.
• I had another person tell me it is the neoprene seal between the outside drive unit and the hull and I should use a silicone to seal.
• Previous owner bypass the key unit and just installed what look like a simple clamp under the dash. Someone said that it is not activating the learning or junior mode??
I did not mine doing all the other stuff since I believe it needed it. I do not however want to continue to replace everything on the boat till it works. This is what is called a parts changer and not a mechanic. I can rip a Harley apart and put it back together blindfolded but this has be baffled. Your help is greatly appreciated in advance.
Hi and welcome to the SeaDoo forum. From what you're saying and since you have replaced the carbon seal and ring, I'm guessing you have a problem with the engine to pump alignment. There is really only one way of checking this, an engine alignment tool. You can purchase one from SBT, they're located in Clearwater FL, also [MENTION=43374]Coastiejoe[/MENTION] will rent you one. BTW a neoprene seal between the pump and the shoe is what Seadoo recommends and what you should use not silicone seal.


I really appreciate the fast response. SBT is less than 10 miles from my home so that is where I have been getting all of my parts. I would agree the motor needs aligned but very minor tweaking I believe. I will get the alignment tool because I am a stickler for things being correct. Please correct me if I am wrong but an alignment off a little should not create a cavitation would it?
Probably not, I'm just going by process of elimination, and if I'm reading your post correctly you've replaced all the drive line components that would cause cavitation. Which leaves only engine to pump alignment or possibly (but not likely) a warped drive shaft.

I'm going to move this thread to the 2-stroke sport boat forum and call on a couple of guys for help, [MENTION=57920]racerxxx[/MENTION] and [MENTION=51350]Jetskigoodies[/MENTION].

Hey Dan,

We had 10-12" of snow yesterday and the city is paralyzed, we haven't had any cars on our street yesterday or today, I shoveled about a 10'x 10' area by the back door so the dogs can do their business and that's about it. When you finish at your house can you come and do mine?


Are you sure you have cavitation? Cavitation feels like if you were in your car and either the clutch is slipping or the transmission is slipping, the engine is operating normally but you are just not going anywhere. In a jet drive watercraft it's caused by introducing air into the jet drive system. Fuel system and ignition problems will not make the boat cavitate.

Welcome to the forum first off. If you haven't already done so, I would at a minimum pull the carbs and clean them. This is something that should not be skipped, there are little filters inside that can clog, restrict the fuel lean out and burn down a cyliner from going lean---not good. If your Neo seal is missing or torn it should be replaced. You can reuse them several time, meaning taking the pump on and off. I would never use silicone to seal it to the pump support, that is just creating a disaster for removal. Also, check the pump shoe that it is sealed to the hull. As seen in the pick with the pink hull, seal the shoe to the hull---I used Ultra black RTV (looks gray). The 3 o-rings you replaced, I'll assume 2 were in the stainless ring and the third was the one that holds it in place after it's together. If that is the case, cut that third one off and use the stainless C-Clip that replaced that years ago. What can happen is the pump pressure can over come what the o-ring can hold and that stainless ring will push towards the PTO on the engine. Also, pump grease into the zerk on the PTO, that will help tighten the stainless ring to the carbon ring. Also, make sure you have both bumpers in the ends of the drive shaft.

Pump shoe sealed


Video of where the C-clip should be and not the o-ring. Part# is listed in my video


Rubber bumpers #12 on the print, 2 per shaft. #2 is the zerk you want to fill. Pump it with grease until it JUST stops moving. About 4 months prego is what the boot (#4) will plump to.

Post a pic of your set up just so we can check it over. If you need help posting a pic, just shout.
I appreciate the fast responses. I hear the north is having it rough with all the snow. Today in Sunny scratch that soaking wet rain it is miserable. I will post pictures as soon as possible. I will put a c cllip in and align the motor this weekend. I work insane hours and do not have any time till the weekends right now. I do however have two questions. My son was with me on my last outing and he believes it is a carburetor problem now since it sounds as though it is flooding when it gets a tad over half throttle. Not sure if I want to try tackle the rebuilding myself, but the dealers are asking for two arms and a leg. Are the rebuilding kits pretty explanatory? I have rebuilt carbs on motorcycles. Also when I replaced the wear ring the new one had a lip on, the old one did not where it fits into the boat. When I questioned this at SBT I was assured this was the correct ring. When I put the ring in I wanted to tap it in securely the last inch and I took a very small piece off that lip. Will this cause a problem? If so I can go in and replace it again. Once again thanks for all you insight.
rebuilding the carbs is relatively self explanatory as long as you are somewhat mechanically minded which you are. If you want to do thorough rebuild you need to buy or build a pop-off tester to check your needle and seat condition, they probly should be replaced if they have a lip/ring around the viton rubber tip, if you ned new n/s be sure to buy needle and seat with the viton rubber tip. also make sure to only buy oem kits, SBT kits have mixed results. As for your wear ring im not sure. . . .but to be safe you could put a small dab of silicone on the area where the ring is chiped and that would solve it I would think. I forget the exact pop off pressures but the service manuel has them im sure. Also always replace carb base gaskets, never reuse. unless they are almost new. Lots of videos on rebuilding carbs on youtube and lots of info here as well anything you get stuck on carb wise im sure is just a google search away :)
I think I will try rebuilding the carbs then. It is funny what you said about using Google, if you cannot find it there you are not looking hard enough. I will try to find the OEM rebuilt kits and do this over the weekend as well as align motor. Once completed I will post pictures of before and after and hopefully a smiley face showing it all worked. If not I will just through my leg over the panhead and ride into the sunset. LOL
Real quick update. A boat mechanic friend of mine took the boat out with me. Took off the air box cover and when I got to the point in the throttle bogging he sprayed just a little starter fluid and the boat took off like it was on fire. Diagnoses is the carbs. Quick question were do you suggest I purchase the carb kit and pump I need to check the psi? I heard that I should stay away from the lower quality vs genuine mikuni. Your direction is greatly appreciated.
You can build your own pump here,
or you can buy one from SBT for $50 im not sure what would be more cost effective, I dont know US prices for those items (Canadian).
I would recommend you open up your carbs first to see if you need n/s assemblies which dont come in the kit, look for a grooved condition on the needle and test the pop-off to see if the n/s is leaking. [MENTION=41828]Minnetonka4me[/MENTION] send him a pm, he has genuine mikuni carb kits and n/s assemblies in stock im sure.

I appreciate the offer and I do need to get some more items can you tell me the best way to get in touch with you?

A quick update is a local dealer had the genuine rebuild kits and I rebuilt both carbs in just over 2 hours. I was not aware that the intake to carb gasket was not part of the kit and those were simple gaskets at 10.00 a piece! I also replace the fuel filters and fuel line completely. Primed the carbs and she fired right up. Took her to a local ramp about 7 minutes away and she ran full speed.

I cannot thank everyone enough for your help and direction.

I have a few small electrical issues I will look for a solution on a different thread.

great job! :) For future reference pick up some intake gaskets from SBT they are only $1 each there, and they are the same thickness as OEM carb base gaskets.
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