1998 seadoo gtx rfi converted to carb.

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Bigproblem

New Member
Purchased this beautiful 1998 gtx rfi back in April. Seller started it right up for me. Me only owning 1 xp prior didn't really know what I was supposed to be looking for. I got it home and started fixing the small oil leak coming for the oil pump. Then I realized things just don't look right in the engine bay. Did some research and found out the seller took all the components out that made it an RFI, and converted it to twin carbs. The 2 most important questions I asked him before handing over 2k were "is it a true rfi?" and "is it water ready?". He replied yes to both questions.

I dropped it in the water when I got home, and it took on a ton of water. Pulled it out and fixed all that. Basically put an entire exhaust on. The reason for that was because he took parts from a few different seadoo's to make this conversion work. The exhaust now was ran on the opposite side of the motor. The same side as the hull exhaust outlet! Anyways, I got that all buttoned up. Replaced all the fuel lines, did a full rebuild the the carbs, cleaned the rave valves, new plugs, etc etc. I ran through basically everything except rebuilding the 787 motor.

I finally got it to stop fouling the plugs and it ran so good for 10 minutes in the water. Then suddenly I felt a big loss in rpm followed by an awful noise from the cylinders. I wrecked the motor. GREAT!

Prior to my test run, I tested the oil pump, replaced and primed the oil lines. I even checked while the carbs were off that the oil was making it to the valve intake cover fittings. Set the carbs to factory 1997 seadoo GTX settings, used the seadoo recommended 2 stroke oil, put the correct spark plug gap and much more.

This was an all summer project. All the research and work I did made me happy for 10 minutes on the water lol.

I'm finding it hard to walk away at this point. Should I find another 787 and swap it out, or do you guys think this Frankenstein of a jetski has seen it's final days?

I'd hate to dump more money into it if this setup just isn't meant to be.

Thanks!
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Pull the plugs,,,do a compression test.
Pull the gray pto cover, does the crank rotate freely by hand?,,,
Pull the pto rave valve, does the piston look scored?
 
Pull the plugs,,,do a compression test.
Pull the gray pto cover, does the crank rotate freely by hand?,,,
Pull the pto rave valve, does the piston look scored?
It had 170 compression on both pto and mag cylinders before I put it in the water. After the loud noise, I pulled the rave valves and noticed the pto side rave had chipped.

Spark plug on the mag side was burning perfect, pto side looked a little wet.

I turned the pto by hand without the plugs in, and it turned without much effort. To much back and forth slack though.

When I pulled the head off, this is what I found.

Worth noting, I found a SBT tag on the head. Previous owner must have ordered a reman motor.
 

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From what you posted you did a very thorough job. Congrats !! Do the checks Popps recomended. Good Luck !!
 
Do you think the PTO connecting rod bearing went south??
I'll pull the jugs off tomorrow and take a small video. It's not costing me anything to tear it down and investigate, so I don't mind.

Do you know what happed with the pto cylinder head and top of piston? I read that it could be caused by water. Like I basically had a steam engine lol.
 
I'll pull the jugs off tomorrow and take a small video. It's not costing me anything to tear it down and investigate, so I don't mind.

Do you know what happed with the pto cylinder head and top of piston? I read that it could be caused by water. Like I basically had a steam engine lol.
Looks lean to me.
 
Looks lean to me.
There's so much to learn here.

On one hand I'm telling myself that the plug was a little wet on the pto cylinder, so it was running rich. Cylinder compression was 170 (tested before my 10 minutes run).

On the other hand it possibly ran lean at one point. I corrected it as best I could, but the pitting damage was already done.

I'm not even sure if "pitting" is the correct word. Looks like someone made a bunch of holes with a punch in a perfect circle.
 
My cousin (very experienced with all engines) tells me that what you are seeing in your case.... at the top of the piston and on the head is aluminum. Supposedly, the cylinder goes lean and the piston gets very hot and turns the aluminum to liquid. That sticks to the top of the head and pulls metal out of the piston. I'm better at looking at pistons to see how they are firing. :) I'm not sure how quickly that kinda damage can take place. Definitely rebuild the carbs.
 
Purchased this beautiful 1998 gtx rfi back in April. Seller started it right up for me. Me only owning 1 xp prior didn't really know what I was supposed to be looking for. I got it home and started fixing the small oil leak coming for the oil pump. Then I realized things just don't look right in the engine bay. Did some research and found out the seller took all the components out that made it an RFI, and converted it to twin carbs. The 2 most important questions I asked him before handing over 2k were "is it a true rfi?" and "is it water ready?". He replied yes to both questions.

I dropped it in the water when I got home, and it took on a ton of water. Pulled it out and fixed all that. Basically put an entire exhaust on. The reason for that was because he took parts from a few different seadoo's to make this conversion work. The exhaust now was ran on the opposite side of the motor. The same side as the hull exhaust outlet! Anyways, I got that all buttoned up. Replaced all the fuel lines, did a full rebuild the the carbs, cleaned the rave valves, new plugs, etc etc. I ran through basically everything except rebuilding the 787 motor.

I finally got it to stop fouling the plugs and it ran so good for 10 minutes in the water. Then suddenly I felt a big loss in rpm followed by an awful noise from the cylinders. I wrecked the motor. GREAT!

Prior to my test run, I tested the oil pump, replaced and primed the oil lines. I even checked while the carbs were off that the oil was making it to the valve intake cover fittings. Set the carbs to factory 1997 seadoo GTX settings, used the seadoo recommended 2 stroke oil, put the correct spark plug gap and much more.

This was an all summer project. All the research and work I did made me happy for 10 minutes on the water lol.

I'm finding it hard to walk away at this point. Should I find another 787 and swap it out, or do you guys think this Frankenstein of a jetski has seen it's final days?

I'd hate to dump more money into it if this setup just isn't meant to be.

Thanks!
View attachment 64138
Make sure you bench test the oil pump,,,it may have failed,,,easy to check.
 
My cousin (very experienced with all engines) tells me that what you are seeing in your case.... at the top of the piston and on the head is aluminum. Supposedly, the cylinder goes lean and the piston gets very hot and turns the aluminum to liquid. That sticks to the top of the head and pulls metal out of the piston. I'm better at looking at pistons to see how they are firing. :) I'm not sure how quickly that kinda damage can take place. Definitely rebuild the carbs.
I fully cleaned and rebuilt the carbs with a mikuni kit. Pop off pressure tested in spec, and leak test passed. Both low and high speed setting were set to a 1997 GTX according to the seadoo shop manual.

The carbs before rebuild were all sorts of off.
 
Make sure you bench test the oil pump,,,it may have failed,,,easy to check.
I hope it didn't fail. I bench tested it when I primed my new oil lines, and it worked perfectly. I also bolted it up and turned the motor over without the plugs in to make sure the oil was making it through the fittings on the intake.

I had a friend hit the start button while I held the pump open and watch the ports. Pump worked as it should.

After installing the rebuilt carbs, I made a really fine cable adjustment to line up the marks on the oil pump.
 
That damage can easily occur from no oil,,,a broken oil line,,, or faulty oil pump,,,
The pieces in the dome could come from either a ring broken, pieces from the rave valve, a bearing from the wrist pin,,,parts of the piston skirt
It is very important that you find the cause of the failure,,, so it does happen again,,, failed oil pumps and blocked carb micro filters are the usual culprits,,, the pumps are hugely expensive,, so guys go to premix after engine failures.
If you get the cylinders bored, make sure to champher the ports,,,I usually use a dremel tool,,, and make sure you get the proper rave valve to piston clearance,,,(think it is .020),, do this with the jugs on a bench,,, way easier,,,
 
Mind you,,, now and then on a “tired” motor,,, good old fashioned metal fatigue can be the culprit if there are no other obvious signs.
 
I fully cleaned and rebuilt the carbs with a mikuni kit. Pop off pressure tested in spec, and leak test passed. Both low and high speed setting were set to a 1997 GTX according to the seadoo shop manual.

The carbs before rebuild were all sorts of off.

This didn't necessarily have to happen under your watch. YOu don't know where the engine has been or what happened to it. That kinda damage is not gonna happen without excessive heat. If you'd lost cooling I think the sides of the piston would seize. Hope you get it sorted out.
 
You lost a lower rod bearing.
You can see the slop in the rod and the scuff marks on the rod. It is also what beat up the piston dome and head.
Crank is shot and piston at minimum.
 
You lost a lower rod bearing.
You can see the slop in the rod and the scuff marks on the rod. It is also what beat up the piston dome and head.
Crank is shot and piston at minimum.
Thank you for watching the video. I'll be pulling the motor to tear it down.
 
Yep, Rod Bearing is DONE. Complete rebuild is needed.
Thank you. There's a guy selling a 96 GTX for $800 not far from me. Video shows it running out of the water. In all fairness though, so did mine lol.

My 2 options at this time are trying a rebuild on my current motor, or buying that 96 gtx and swapping the motor.
 
From my experience it is better to rebuild the one you have now unless you are unhappy with it. I don't like that yours is a converted ski and in buying the GTX you'll have a running ski right away. The engine rebuild is likely gonna cost you a more than $800 and some time. You can do some checks on the ski before you buy it. Expecially a compression test, look at the impeller wear ring, make sure the electronics and starter are working well, and inspect the hull and gauges. Working gauges are getting more and more expensive.

I buy Seadoo 2-strokes jet skis to restore and they all need a lot of work (more than can be imagined). I've paid more than $800 for a ski with a bad engine so you might not be getting much for that kinda money. At present consider that every ski you buy needs an engine or will need one soon. I've met people that spent $3000 and gotten a junk ski. Whatever you choose, just enjoy the journey and don't think about the money. New skis are over $10k so you're getting the same fun for a lot less $$. Good Luck !!
 
From my experience it is better to rebuild the one you have now unless you are unhappy with it. I don't like that yours is a converted ski and in buying the GTX you'll have a running ski right away. The engine rebuild is likely gonna cost you a more than $800 and some time. You can do some checks on the ski before you buy it. Expecially a compression test, look at the impeller wear ring, make sure the electronics and starter are working well, and inspect the hull and gauges. Working gauges are getting more and more expensive.

I buy Seadoo 2-strokes jet skis to restore and they all need a lot of work (more than can be imagined). I've paid more than $800 for a ski with a bad engine so you might not be getting much for that kinda money. At present consider that every ski you buy needs an engine or will need one soon. I've met people that spent $3000 and gotten a junk ski. Whatever you choose, just enjoy the journey and don't think about the money. New skis are over $10k so you're getting the same fun for a lot less $$. Good Luck !!
I like everything about your comment. I'll rebuild because now I have all fall, winter and spring.

I remember now why guy wouldn't take my motor as a core. He said its because SBT flap wheels the mating and gasket surfaces.
 
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