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  1. #1

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    I think I need a fuel pump?

    '96 780 running gear in a '95 SL750 hull. I finally got everything changed over which included all new fuel lines, new fuel shutoff valve, new piston in PTO cylinder. Went through the carbs and replaced all the needle valves(two were leaking). Got it all put together, fired right up after priming the fuel. Started it on the hose and found a water leak at the manifold. I reused the gasket so that was my fault. I got the new gasket installed today and went to try it again and now I can't keep the fuel strainer full. I did find a loose fuel line at the pump for the PTO cylinder when I was taking the exhaust apart. It was loose enough to bleed off some pressure and leak a bit so thats the only other thing changed since before the exhaust leak. I checked the tank vent and its clear. Pulled one of the feed lines at the carb and cranked it over and I get pulses of fuel. I can remove a fuel line upstream from the pump and use a primer bulb to pull fuel from the tank with no difficulty. If I let it sit a minute the fuel filter and strainer will fill but as soon as I start it, they empty and it runs rough and I shut it down. I removed the return line at the tank and haven't seen any fuel flow there. The orifice was clean when I had the carbs apart and the fuel pump impulse line held 5 psi of pressure like the manual mentions. I had it apart too and it was clean. So, what do you guys think? I don't have a spare triple outlet to try and I am warry about using one of the single outlets lying around somewhere. I realize that $25 for a new pump from John Z isn't anything to worry about, but I would like to try to eliminate anything I am missing so that this thing might see the lake before the weather gets cold.


  2. #2
    johnsonmtz's Avatar
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    780 carb rails aren't plumbed for a single outlet pump. They are set up for a triple outlet pump to maintain adequate fuel flow.

    The lack of a full strainer sounds like an air leak somewhere. Check all your fittings in and around the tank to make sure you aren't sucking air anywhere.

    Order a triple pump from John Z and install that before you run.

    KJ

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Are you using the 780 pentagon triple outlet fuel pump?

    Check your hose connections. It sounds like something is not correct.

  4. #4
    ujustlost's Avatar
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    check and see if the o-ring where the bowl of the water/fuel separator screws on is missing. If you do think its a fuel pump issue, I would rebuild the one you have, rebuild kits are less than $10 on ebay and they are ridiculously easy to install.

  5. #5

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    X....I am using the pentagon pump that came with the 780. All connections are tight, no air leaks that I can tell. When I let it sit after cranking, the clear fuel filter I am using fills with fuel from the strainer canister until it uncovers the pickup. Also, there is six gallons in the tank.
    The canister o-ring is in good shape.

    John Z is sending a pump free of charge to cover an issue I had on another order so rebuilding it doesn't make sense. Talk about awsome customer service.

    For some reason I feel like I have a vent problem as well. Should the tank have pressure in it........hiss from the filler when the cap is loosened?

    Thanks for all the good ideas so far.

  6. #6
    johnsonmtz's Avatar
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    Quote Originally Posted by bigboatman View Post
    X....I am using the pentagon pump that came with the 780.

    For some reason I feel like I have a vent problem as well. Should the tank have pressure in it........hiss from the filler when the cap is loosened?
    Okay, if it's the pentagonal 2-outlet pump you should be fine.

    Yes the tank should have some pressure. The vent allows air IN to displace the fuel that is used, but it does not allow pressure to vent out.

    KJ

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by bigboatman View Post
    ...When I let it sit after cranking, the clear fuel filter I am using fills with fuel from the strainer canister until it uncovers the pickup...
    What do you mean, the fuel filter fills with fuel?

    It should always have fuel in it, right?

    Are you saying the fuel drains back into the fuel tank?

    That may imply you have an air leak in the fuel lines, or seals.

  8. #8

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    There is basically what amounts to an air bubble between the fuel filter and strainer. I need to get a pic of this and post it, it would make more sense if you could see my fuel line routing. The engine will run on whats in the fuel filter, but it doesn't refill fast enough to stay running. That is at idle by the way. When I shut it down and let it sit, the strainer level decreases and the filter fills back up. The strainer is pre fuel valve and the filter is after the valve and before the pump. I will try to add a pic to this when I get home from work.

  9. #9

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    Here is how I have it set up. You should be able to see the air pocket in the strainer and fuel filter. Thats the most the filter has ever filled. I am kinda confused now, maybe I do have an air leak somewhere. All connections are tight and everythings is basically new. I will have to check the strainer gasket again I guess.


  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Ditch that in-line filter. The water seperator has a filter in it.

    You're actually making a restriction by using it AND the water seperator filter.

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