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  1. #1

    96 GTX - Rebuild + Oil Problems

    We have had trouble with this skis engine, and I would just like to cover some things before we take it out this summer and end up destroying an engine.

    We have a 96GTX 787 type engine.

    A month ago we pulled the engine and put bumpers on the drive shaft ends as the shaft was walking and letting air into the pump assembly. This now looks fixed (one of the bumpers was missing).

    While the engine was out we pressure tested both cylinders finding that one would hold 50+ psi and the other would leak at 11psi we decided to pull the top half. The was scaring on the back cylinder (if the engine was still in the ski). So the sleeves (I think) are getting rebored and we purchased new pistions from SBT.

    http://www.shopsbt.com/seadoo-jet-sk...it/60-107.html

    Since our current engine is a rebuilt one from SBT it was at a 1.0mm oversize, so our new pistons are a 1.5mm oversize.
    • What precautions should we take after the rebuild? Should the ski be broken in again?
    We were running 40:1 premix with this ski and the engine lasted 2 summers. Obviously we are doing something wrong.
    • We are using generic oil from what I hear the 787 engine doesn't like this if so what type of oil should we use?
    The Oil pump is functional (just tested it with a drill this morning) it pumps oil fine (not sure about it pumping into the injectors though).


    • Should we stay premix or go back to using the oil pump, I have no trouble checking the oil lines before launching the ski is there anything else to check to make sure its doing its job?
    • Also, is it possible that you can over oil the 787 engine?
    • I read something about a 2/3 throttle lean spot with this ski should be concern me?
    • While the engine is out, anything we should check / do to the ski?
    Thanks for helping out!
    ~Karl

    Edit:

    Since the engine was out we did the following:

    • Rave Valve bellows was folded in on it self. The rubber was shot, we purchased new parts for the RAVE assembly with the exception of the metal pieces as they looked clean, wiped a little oil off of them
    • Re-filled the grease fitting on the drive shaft -> motor there is a Zerk Fitting there
    • Cleaned the inside with dawn soap
    I am heavily leaning toward leaving it premix, as mixing on the water is not a problem.


  2. #2
    canuck's Avatar
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    I'll answer in point form, all my opinion.

    - For the driveshaft problem replace the carbon ring and rubber accordion boot as the boot ages is does not hold enough pressure on the carbon ring and can leak air when WOT from a stop.

    - For oil use a good quality synthetic two stroke oil designed for RAVE valve motors, Seadoo XPS, Amsoil Interceptor or something similar.

    - I personally have never had an oil pump failure on a Seadoo and prefer to keep the oil injection system vs premix. I'm no expert on premix but I believe you need to richen up the carbs as the oil in the fuel actually reduces the amount of fuel in the cylinders and cause it to run lean.

    - Rebuild both carbs with Mikuni kits, replace all of the gray fuel lines and make sure the fuel selector valve is not clogged. Seadoo changed the carb settings on the 97 GTX as they were having problems with the 96s, same machine different carb settings. The 96 calls for the high speed screws to be closed on both carbs on the 97 the mag carb is closed and the PTO carb is 1/2 a turn open. On mine I installed Prok flame arresters and rejetted the carbs and it feels like better throttle response off idle. These are the jetting specs I used http://www.greenhulk.net/forums/showthread.php?t=170813

    Good Luck

  3. #3
    Quote Originally Posted by canuck View Post

    - For the driveshaft problem replace the carbon ring and rubber accordion boot as the boot ages is does not hold enough pressure on the carbon ring and can leak air when WOT from a stop.
    We have a new carbon ring (but looks nearly identical to the one thats on it) as we replaced that one last year hoping to fix this issue. I also changed out that rubber boot this year although it also didnt seem much different. But when I pulled the engine the rubber bumper that is on the end of the drive shaft was missing, allowing the shaft to slider up into the motor by 1/2". Now that the bumpers have been replaced the slip ring -> carbon ring -> Rubber boot -> Hull is super tight.

    Quote Originally Posted by canuck View Post
    - For oil use a good quality synthetic two stroke oil designed for RAVE valve motors, Seadoo XPS, Amsoil Interceptor or something similar.
    I was mistaken and we are using Seadoo XPS oil. So that should be fine, from what I read around here?

    Quote Originally Posted by canuck View Post
    - I personally have never had an oil pump failure on a Seadoo and prefer to keep the oil injection system vs premix. I'm no expert on premix but I believe you need to richen up the carbs as the oil in the fuel actually reduces the amount of fuel in the cylinders and cause it to run lean.
    I have not tuned the carbs but my brother rebuilt them with the Mikuni kits, and they seem to be working better, but could this cause less oil to be in the engine? Or too much and cause other problems?

    Quote Originally Posted by canuck View Post
    - Rebuild both carbs with Mikuni kits, replace all of the gray fuel lines and make sure the fuel selector valve is not clogged. Seadoo changed the carb settings on the 97 GTX as they were having problems with the 96s, same machine different carb settings. The 96 calls for the high speed screws to be closed on both carbs on the 97 the mag carb is closed and the PTO carb is 1/2 a turn open. On mine I installed Prok flame arresters and rejetted the carbs and it feels like better throttle response off idle. These are the jetting specs I used http://www.greenhulk.net/forums/showthread.php?t=170813

    Good Luck
    As noted carbs were rebuilt last year, we opened and cleaned them out after it started to backfire a little bit at the start of this year. The fuel selector valve was replaced last year as well at the same time our fuel filter and all our fuel lines were. We now have black fuel hose and nothing grey in the ski.

    Thanks for the ideas

  4. #4
    surferd15's Avatar
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    The 96 has a O-ring on the driveshaft that holds the metal ring that rubs on the carbon, they are known to fail and cause the metal ring to slip forward causing a leak and cavitation, replace it with the updated metal ( half moon shape) c clip. SBT always bores their engines to 1.0 so your stuck with buying parts from them to make it over that size or resleeve...I personally would not run an SBT engine or a top end...but thats my opinion. You WILL have to go through the break-in period again. I have tried two techniques of breaking in, the easy way and the harder way. The engine that was done the harder way runs way better and is more powerful. I believe that your rave valves will need to be clearanced again for the 1.5 over pistons. If they are not they can get caught on a ring and there goes your new topend. The 96 also uses non-slotted raves which can stick and also crack and fall into your motor (happened to me) its good to replace them if you want with the newer ones SBT sells with slots in them. The newest rave bellows are the green ones. Oil wise Seadoo full synthetic and Amsoil Inter. are thes best. I have had an oil pump come loose and lost an engine but I prefer still to use injection. Attach a drill like you stated before and when the carbs are removed you can see it inject oil out of the injectors, or better yet just pull the spark plugs wires and ground them on the rear e-box, hold the throttle wide open and crank the motor you should see oil come out. The oil injected has nothing to do with carb settings, however there is an adjustable oil line-on the pump there is a line that needs to be matched with the line on the throttle linkage-check this to be sure its getting the right oil. First tank on break in is premixed, rest are not. Since you rebuilt the carbs what is your pop off set at? If its off it will cause problems. I would def do a plug chop on wot and slow speed to dial your carbs in. I have owne 2 96 GTXs and a 97, loved em all! My 97 had over 600 hours on it, looked pretty good and ran 54.8 gps!

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