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Thread: Newbie - SLX780

  1. #1

    Newbie - SLX780

    Alright, I'm guilty....this was a total impulse buy. I have zero pwc experience but I am comfortable doing most jobs on my bike and jeep.

    I came across it this weekend at an estate sale. Previous owner passed away.
    I got it for a steal. Heres what I know.

    12 hours according to the Display.
    1995 Polaris SLX 780 (came with a triton galvanized trailer). Both titled, I was the winning bid at $350.

    While I know the hours could have been reset, the condition of the engine compartment, gaskets, carbs, etc leads me think that maybe...just maybe this thing really does have 12 hours on it. But who knows.

    I know that it's been sitting for two years and was winterized before being put away. I bought it with no battery. Brand new impeller and the fuel pump was replaced 3 years back according to receipts. Looks like it's been well cared for and stored indoors.

    Went out, bought a new battery. Charged her up and as much and she tried, just wouldn't turn over.

    Sparkplugs had a little oil on them, but cleaned them up and spark was good. I'm waiting for my compression tester to arrive but all pistons are firing with enough force to see air moving. (if that makes sense).

    The gas/water separator does not seem to be filling up with gas which leads me to believe this is a fuel delivery problem. (Yes, I have the fuel valve on the exterior of the craft turned to the on position)

    I traced the power from the sending unit in the gas tank to the electrical box, test for power and voltage seems fine. Though the sending unit doesn't click or pump with direct current applied.

    Couple questions.....

    1) any comments on the ski in general? I've been looking around in the forums here and seems to be a few people that have good things to say about it. anything I should be particularly careful about? any comments based on the pics?

    2) I read about a CDI upgrade / update. Is there anyway to tell if this has been done to this ski? (Pics attached).

    3) I also read about fuel delivery upgrade/update. Based on searching the forums here, looks like it basically takes fuel delivery from a single rail into individual feeds into the carbs. If so, looks like this has been done already on this boat. Am I correct? Again, applied direct current to the fuel sending unit and didn't hear any clicking or anything. Am I correct in assuming this thing has failed?

    4) My 2 stroke experience is somewhat limited, can I pour a little gas into the cylinder to get her started? Or is this a no no? (Guess a temporary test before getting a new sending unit to see if I can get the engine turned over).


    Also, can I remove the cylinder covers? Gaskets seems to be in good shape, will I need to replace them if I do remove the cylinder covers?

    Thanks in advance, I know it's a lot of information but thought better too much than not enough!












  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk Chicago.

    Is that your location? We have a few members in that area that may be able to lend a hand if needed.

    First, define as much as she tried, it wouldn't turn over. Because you will not get spark if it didn't turn over.

    Second, the sending unit is not an electric fuel pump. It just sends a signal to the gauge to show fuel level.

    I'm surprised to read that the fuel pump was replaced. The 780 came from the factory with the H.O. triple fuel pump already. You can get a rebuild kit for much cheaper than having to replace the fuel pump.

    It sounds to me like there was a fuel delivery issue to begin with.

    The fuel pump is driven off of pressure and vacuum created inside the crankcase. There's a diaphragm that moves back and forth depending on the PTO cylinder (rear) stroke. That diaphragm movement "pulls" fuel from the fuel tank, and "pushes" it through 2 check valves inside the pump towards the carbs. At the end of the carb rack is a TINY .018 orifice that creates the fuel pressure for the carbs, and any excess fuel is returned to the tank.

    1. It's a great ski, should be fun and pretty quick for your first ski. Around 52-54 MPH at 6500 RPM. The fuel system is the weakest part of these engines. Make sure the fuel system is clean and clear to prevent fuel restriction. That will result in a damaged piston or pistons.

    I'd suggest replacing all the fuel hoses and in line fuel filters. Inspect the water seperator for any clogs. Open up the petcock and inspect it for signs of restriction. SERIOUSLY consider going through the carbs completely and inspect the filters inside them. Finally, replace the pulse hose going from the engine block to the fuel pump. If you see signs of fluids inside the hose, then you may want to open the fuel pump for inspection. If fluid is inside the diaphragm area, your fuel pump signal will be severly weakened. (I know it sounds like alot, but you're only looking at $35 or so of fuel hose, filters, and carb base gaskets. The rest is only your time and labor)

    2. It does not appear that the upgrade was performed to the CDI. But can you please tell me what the printed numbers are on the black CDI box inside the elec. box? The upgrade was for an intermittant hard starting condition.

    3. Your fuel system is upgraded. Just replace the hoses and filters as mentioned before.

    4. Yes, pour a little premis 40:1 down the carb throats to prime the engine. This will also help aid in the fuel lines getting primed and reducing the wear on the starter.

    5. Yes you can remove the cyl heads. But, you will want to get new head gaskets. Some of us have re-used them by spraying them with 3M copper spray, but I don't suggest that. (even though I'm guilty of it)

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome to the Hulk

    As xlint said, the fuel sender is just a LOW VOLTAGE sender for fuel level. The fuel pump is mechanical, not electric. Applying 12 volts to the sender may have damaged it

    In any case, fuel level sender problems will not affect engine starting.

    The Ignition System Update Kits only apply to the red domestic engines, not the blue Fuji engines.

    I think that Triton trailer is aluminum, not galvanized.

    If you remove the fuel feed hose at the fuel pump inlet, and apply some vacuum, does fuel flow?

  4. #4
    LaveyT's Avatar
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    Thumbs up Good Info here!

    Welcome,
    That is my favorite ski by far. Good luck and have fun!

  5. #5
    xlint & K447 - thanks for info, I really appreciate the quick response.


    Quote Originally Posted by xlint89 View Post
    Is that your location? We have a few members in that area that may be able to lend a hand if needed.
    Yep, I'm on the far north side of the city, right next to the lake. Would welcome any help with wide open arms and a six pack if I can't get this beast to turn over!

    Quote Originally Posted by xlint89 View Post
    First, define as much as she tried, it wouldn't turn over. Because you will not get spark if it didn't turn over.
    Well, I can hear the pistons pumping. I know every sparkplug has spark, when grounding the plug above the piston and cranking the engine I can see it sparking. I can hear the starter chugging away, sounds like it wants to go but it just keeps cranking and pistons keep pumping. Think this is a lack of fuel getting to the pistons. Pistons "seem" like they have good compression (though I don't have my tester yet).

    Quote Originally Posted by xlint89 View Post
    Second, the sending unit is not an electric fuel pump. It just sends a signal to the gauge to show fuel level.
    Quote Originally Posted by K447 View Post
    As xlint said, the fuel sender is just a LOW VOLTAGE sender for fuel level. The fuel pump is mechanical, not electric. Applying 12 volts to the sender may have damaged it.
    Great, I swear to god I thought this as I was putting the leads on. Hopefully not, I had the foresight not to hook it up to the new battery but rather an older sealed rechargeable unit from a UPS with lower voltage (7.2 I think?).

    Quote Originally Posted by xlint89 View Post
    I'm surprised to read that the fuel pump was replaced. The 780 came from the factory with the H.O. triple fuel pump already. You can get a rebuild kit for much cheaper than having to replace the fuel pump.
    No clue, "fuel pump & install" is what the receipt reads. Guess that could be anything.



    Quote Originally Posted by xlint89 View Post
    The fuel system is the weakest part of these engines. Make sure the fuel system is clean and clear to prevent fuel restriction. That will result in a damaged piston or pistons.
    Best way to go about checking for restriction is applying vaccum after the fuel pump (which I now now is manual) and before the engine?


    Quote Originally Posted by xlint89 View Post
    I'd suggest replacing all the fuel hoses and in line fuel filters. Inspect the water seperator for any clogs. Open up the petcock and inspect it for signs of restriction.
    I definitely will replace all lines and filters. Newbie question I know, by petcock to you mean the fuel on/off switch at the outside of the hull?


    Quote Originally Posted by xlint89 View Post
    2. It does not appear that the upgrade was performed to the CDI. But can you please tell me what the printed numbers are on the black CDI box inside the elec. box?
    Best I can tell it looks like these numbers (dashes are illegible numbers)

    20_ _
    8 _ 33071
    5318
    78W95




    Quote Originally Posted by xlint89 View Post
    5. Yes you can remove the cyl heads. But, you will want to get new head gaskets.
    Searching the forums I see that a Mr. Zigler is a good resource for parts? Do I just PM him with what I need?



    Quote Originally Posted by K447 View Post
    I think that Triton trailer is aluminum, not galvanized.
    I think you're right. Documentation for the estate sale said galvanized, I was thinking that as I put it into my garage!

    Quote Originally Posted by K447 View Post
    If you remove the fuel feed hose at the fuel pump inlet, and apply some vacuum, does fuel flow?
    Do you mean here (where yellow dot is)?






    Big thanks to both of you! I really appreciate the help and can't wait to get out on the water!

  6. #6
    Quote Originally Posted by LaveyT View Post
    Welcome,
    That is my favorite ski by far. Good luck and have fun!
    thnx!

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