Default 750SXI Exhaust Cooling problems

Discussion in 'Tech Discussion' started by orac12, April 20, 2015.

  1. orac12

    orac12 New Member

    I've got a 750SXI Pro I got second hand and don't know too much about but it seems to have a lot done to it.

    R&D Head
    Factory pipe dry pipe
    Skat trak intake scoop
    Jet unit appears to be modified as well and has something written on it about 82mm reduction

    After a bit of work its been running well, but the other day it suddenly got louder and exhaust water box getting sizzling hot. I suspect no water going through the exhaust.

    Cooling system appears to be modified and has two water supplies from the jet unit (i believe they only have one standard).

    First feed goes to the engine block, then from the top of the head there is two lines for the tell tales with a third going to the dry pipe which then exits from the dry pipe and goes out a third tell tale.

    The second feed goes to the exhaust manifold, i'm not quite sure how this works but I assume it injects water into the exhaust manifold which goes through the exhaust, the waterbox and out with the exhaust gases, this keeps the exhaust cool and also quietens the engine.

    I have blown air down all the cooling lines and none appear blocked. To me these two cooling feeds should be seperate from each other, but when I blow air up the feed for the exhaust manifold I am getting air out of the two tell tales from the cylinder head and i'm not sure how its getting there. To me they shoud be seperate?

  2. dickwebb

    dickwebb Active Member

    Hmmm... I know all about this ski. It was a weapon.

    Dual cooling from the pump is a very common mod. Especially with a big dry pipe, and higher comp head. They do only have one from standard but you definitely need two on a setup like that. Nothing to worry about.

    Where does the first feed go into the cylinder block - from memory it should be between the exhaust outlets on the block? That is OK. It is an old-school kawi mod for additional cooling when running the aftermarket exhaust systems.

    With the second feed as you've described that goes to the exhaust manifold. The manifold is jacketed (like the cylinder) and has an inner liner that fills with water to keep it cool. The water will pass from there, through a few holes in the exhaust gaskets, and into the cylinder as well. It does not inject water into the exhaust at any point there. Usually this is the primary route for water on a single line system. All skis will have their water line from the pump, to the exhaust manifold, which will then feed through to the cylinder and out. Thus this, and the incoming water line feeding the cylinder directly, are all on the same system. This is normal.

    The exhaust system you have is a dry pipe. Which, unlike standard factory exhausts, doesn't get water cooled in the initial stages. The whole chamber (silver chamber) is completely water jacketed. This allows the exhaust to stay hot and dry but within required temps. Gives you more HP at higher RPM. So, since your exhaust isn't getting hot (it'll get warm) there is nothing wrong here.

    The issue you have is that the line that comes off the top of the chamber (the faded clear hose in the pic) takes water from the water jacket of the chamber and feeds it into the exhaust, or stinger section, and it is then piped down to the waterbox. This is done to cool the exhaust gases before they reach the water box. If you disconnect that line at the top of the chamber I doubt you'll be able to blow through it. There is a little jet in the connection at the exit of the chamber (where the other end of the pipe connects to) and that will be blocked. Thats why the waterbox is getting hot.

    You'll be hard pressed to get it fixed without taking the chamber off but at the same time those chambers are a right pain and hard to seal up when going back on. All you need to do is unblock the jet and away you go. From memory the jet is a high-speed mikuni carb jet around 150 in size.
  3. orac12

    orac12 New Member

    Your explanation of the cooling system has certainly cleared things out, I just came back to check this thread after finding the nozzle in the stinger section blocked with sand! Easy fix, and you were bang on.

    What else do you know about this ski? It appears to have a modified pump and few other things. Im having a few other issues with it, I cannot stop it from porpoisoing but maybe that is just me.

    Also, at low speed / when taking off I really have to feather and pulse the throttle to get it going otherwise it just revs up and cavitates... I was thinking it could be the way the pump is setup, or it is sucking air from somewhere (pump shaft seal?)

    Anyway, first pole ski and im still learning on it has been great fun so far though.
  4. dickwebb

    dickwebb Active Member

    Yeah, I know a fair bit about it. Pump itself isn't modified but the reduction nozzle has been bored (another relatively common mod) to give it a bot more snap on the bottom end. It'll have an aftermarket prop etc as well.

    Not sure what ride-plate is fitted to it now. If it sticks out the back a good 100mm then you've got the best you can do for the porpoising. Ride time will fix that. You can also take the ride plate off and fit 1-2 2mm washers under the two rear bolts of the ride plate. That will force the nose down a little more in the chop. But don't rip into a high speed corner as it'll bury the nose easy :)
  5. orac12

    orac12 New Member

    Yeah its got a purple ride plate with a "d cut" that sticks a fair bit out the back.

    What about the low speed cavitation?
  6. dickwebb

    dickwebb Active Member

    Yeah most likely it is the pump seal, and/or the prop is super damaged. Most likely the pump is not sealing because the seal is stuffed. Easiest way to check is pull the ride plate and intake grate off and take a look. If the props been changed then it could be that but I'd be leaning towards the seal in the first instance.
  7. orac12

    orac12 New Member

    Looking through the intake grate and into the nozzle the impeller looks fine and it does leak water into the hull past the shaft when not moving. Is it a big job to remove the pump and do the seals and bearings? Was looking at this kit:

    Then removing the ride plate and pump, checking the impeller while its out then doing the bearings and seals, hopefully ready for the weekend.
  8. orac12

    orac12 New Member

    Pump and engine out. Seals are fucked, could see daylight past them. The seal housing is also corroded and rooted, where is a good place to get a replacement?
  9. dickwebb

    dickwebb Active Member

    Yep, you'll need that a kit but not that one. This one:

    750 SXi Pro has the same pump as the SXR 800.

    Everyone will say "stick to OEM" when it comes to seals etc and usually I would say the same. In this case Kawi parts aren't as common on here as Yamaha etc. And realistically the aftermarket stuff has improved so I don't think you'll have an issue. Plus Cathie will give you a Dalusion discount usually. Roger (JetWerks) may also have a kit.

    Getting a pump seal (the seal that goes around the outside of the front of the pump) will be a little bit more difficult (I'm assuming thats stuffed too). The Kawi P/N is 39145-3735. I'd either ask Cathie @ JetSkiJunk and they may have one or call Steve Amende at Otago Personal Watercraft ( He's a Kawi dealer and is most likely to be able to post one up asap.

    Re the corrosion on the seal housing. I'm assuming this is in behind the impeller where the seals are before the bearings? Depends how bad it is. Most will say get a new pump and possibly you could get one cheap but if the corrosions not too bad I'd (and its a bit of a rough suggestion) but try some good marine adhesive sealant (like Sika MS1) on the outer edges of the seal as you press them in. If the corrosions on the outside of the pump where that outer seal goes between the pump and the hull a little of the sealant wouldn't go a miss there either.

    Post some pics just in case
  10. Flan

    Flan Well-Known Member

    should have purchased a superjet. You will fix the sxi pro sweet and two rides later it will die again. Yer im a hater.
  11. dickwebb

    dickwebb Active Member

    and also never owned an SXi Pro....
  12. orac12

    orac12 New Member

    Been out on it heaps with out any issues.. Wouldn't mind something a bit more modern later on though when I get better at it.
  13. Flan

    Flan Well-Known Member

    Na but Beronski did and all they did was break down. Then he got a 800 and that sunk and was never found again.
    Glue stick had a sxi the pump fell out on the way to the surf.
    Sorry Dan(taupo dan) he has a kwaka engine in his and both FOFs it has broken down.
    How many kwakers are in the surf. OH F all.
    My 1996(touch wood) super jet still going strong.
    Kwaka should just make bikes. but even there average.
  14. dickwebb

    dickwebb Active Member

    Stop drinking and posting Flan.

    If you look after it you won't have too many issues. Not the best handling hull for surf riding but if you learn to ride that well, then you can ride anything.
  15. orac12

    orac12 New Member

    Rubber bearing housing is attached to this aluminum housing which is fucked. Is the alloy housing a factory part and where can I get one? I don't see it on any part diagrams.

  16. dickwebb

    dickwebb Active Member

    Shit. Not as bad as it looks.

    The black plastic/ali bearing housing should separate from the corroded aluminium plate/cone section at the rear which is heavily salted up. Its just siliconed on to seal it up. Get them separated apart. Looking at it from the pic I don't think you need a new one. That plate/cone (which I have never seen come out before on any kawi hull) needs to be cleaned up (say give it a sand/bead blast and a quick spray of paint) and glue it back in. I'd probably use a good marine adhesive/sealant again and don't be shy. Its not overly important apart from providing a nice surface for the bearing housing to seal to.

    For that bearing housing, if you need new seals/bearing for that then you need this kit.

    Rebuild it and then to align it you do the following:

    1. Put the pump back in after a rebuild.
    2. Put some good quality silicone on the rear of the driveshaft bearing housing and slide it onto the driveshaft and all the way up
    3. Put the driveshaft in, through, and into the impeller. Don't push the driveshaft bearing housing back onto the bulkhead yet.
    4. Put the engine in and slide it in so the couplers mate.
    5. Now slide the driveshaft bearing housing back and do it up onto the bulkhead sealing it to the plate and hull. Done.
  17. orac12

    orac12 New Member

    Sweet, thanks for the tips on aligning it all. That plate is pretty rooted, if I sand blasted it there would be nothing left, it's gone soft and porous. I'll make a replacement from stainless.

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