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  1. #31

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    Still working on it but have had some success, see my post above
    Quote Originally Posted by Atmosphere View Post
    Sorry guys I have not been able to get any work done since my last posting due to family matters! And won’t be able work on it for a few more days. I have picked up another o-ring for the separator but have not had a chance to swap it in or vacuum test the lines & tank.

    Waterpest, definitely let me know if u figure out your problem! Only difference is my tank builds pressure when sitting in the heat and I get a whoosh of air out the cap.

  2. #32
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Lots going on in here now.

    I would be very surprised if you can blow through the pressure relief valve. It requires 2 PSI to open. How easy does it open?

    If it opens easily, you're most likely not developing any pressure to help push the fuel to the pump.

    First off, the operating range of the 780 engine is 6500 RPM. If you're only seeing 6240 RPM, you're still not running correctly. What does your piston wash look like?

    I am very confused on why you guys are not filling the water separators. I'd love for someone to be able to figure this one out.

    If you're not filling the separator, you're most likely not getting full fuel flow to the carbs. So, yes, you will not get high RPM.

    I am not sure why you would fill the bowl over night. It seems to me everything would cool down over night reducing pressure.

    Are you sure your fuel pump hoses are installed correctly? Can you please post a clear picture of your fuel hose routing.

  3. #33

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    I could not blow through the pressure relief valve, hence complete testing will occur when I receive the MityVac. I could blow through the air inlet valve in the direction to the tank only. I had just rebuilt the carbs and only ran a tank of gas through the ski and I set the highs a little fat to dial them in but that hasn't happened yet due to the fuel bowl air issues. I did get a couple piston wash photos
    I am using a round SLT750 MFD as my Oval MFD is dead...I assume the rpms are displaying correctly.
    I didn't think 6240 rpm was full out....
    I am away from the ski until after the weekend so I cannot post a photo of the fuel pump config...Question: I see the Polaris manual shows fuel lines for each carb fed from a specific fuel pump outlet, does it matter which carb is fed by which specific fuel outlet? I know the carbs are all fed by "outlet" nipples, and that the pulse and feed are correct. All lines are Marine USCG approved 1/4" new, pulse line is the recommended length.

    What puzzles me is that the engine will run at all with over an inch of air in the fuel bowl....the inlet at the top in the casting is exposed to air, how does fuel get to the pump? I have watched the fuel bowl, engine revving to 4500rpm pump in the water ski strapped, to my lift, and the fuel level was JUST above the lower metal rim of the filter....The separator casting is well marked, the in and out lines are good.


    Quote Originally Posted by xlint89 View Post
    Lots going on in here now.

    I would be very surprised if you can blow through the pressure relief valve. It requires 2 PSI to open. How easy does it open?

    If it opens easily, you're most likely not developing any pressure to help push the fuel to the pump.

    First off, the operating range of the 780 engine is 6500 RPM. If you're only seeing 6240 RPM, you're still not running correctly. What does your piston wash look like?

    I am very confused on why you guys are not filling the water separators. I'd love for someone to be able to figure this one out.

    If you're not filling the separator, you're most likely not getting full fuel flow to the carbs. So, yes, you will not get high RPM.

    I am not sure why you would fill the bowl over night. It seems to me everything would cool down over night reducing pressure.

    Are you sure your fuel pump hoses are installed correctly? Can you please post a clear picture of your fuel hose routing.
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  4. #34
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Everything sounds correct, but there's something we're missing.

    Shouldn't matter which fuel pump supply hose goes to what carb. I just need to see your set up please.

    You don't have any hoses that can be kinked or pinched I'm assuming.

  5. #35

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    All the hoses are routed where they should be, no kinks. Received a defective MightyVac yesterday...its going back to Amazon. Replacement should arrive tomorrow, I will vacuum/pressure test with some Snoop and I will get you a photo Sunday or Monday(Vacation Yay!). I think that Piston wash looks ok?
    Thx for your help all
    Last edited by waterpest; 07-24-2019 at 10:37 AM.

  6. #36
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    The wash in that particular pic looks fine. But that's only 1 of 3 cylinders.

  7. #37

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    xlint89: I will get more photos of everything you want to see by Monday latest


  8. #38

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    I bypassed the fuel selector with 1/4 inch Barbed fitting, did a test run and with the fuel bowl full is hitting 6400 RPM, machine is running phenomenal, I realize I'm missing 100 RPM, could be that I'm running a tad rich on the highs??, prefer to leave it that way since my kid likes to do extended wide open runs, feel a little safer running rich. Lots of piston wash, plugs are tan to dark tan. I pick up 50 rpm in a hard right turn, lose 100 in a hard left turn...

  9. #39
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    If wash show really rich, lean it out some. You should be able to run 6500 RPM safely.

    If you want to be safe, keep your wash about thumb nail sized as opposed to pinky nail. Should reach 6500 RPM and still be safe from extended long runs.

  10. #40

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    Thx xlint89....I have been running it for a week and a half now on Vacay, my endoscope broke so I cannot see the piston wash but the max rpm is still 6360-6400. There is a time lag between 5700-6360 rpm. Most times it takes 7-10 seconds to get to max rpm from 56/5700 rpm at WOT unless I crank a hard right turn(which is very tight with my custom Sponsons installed) then it pulls very linear and hard and will climb to 6400 rpm after 2-3 seconds of WOT...Feels just like that powerband pull around 4700rpm. Dream-o-meter maxed at 50.2 mph, Gps is showing 48.9 mph. Plugs do not look overly rich, in fact they seem to show lean so I did richen the highs 1/4 turn to darken up the plugs some....Maybe I am running too rich still?? Are the rpm gain/loss symptoms during turns a reliable tuning pointer??

    Quote Originally Posted by xlint89 View Post
    If wash show really rich, lean it out some. You should be able to run 6500 RPM safely.

    If you want to be safe, keep your wash about thumb nail sized as opposed to pinky nail. Should reach 6500 RPM and still be safe from extended long runs.

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