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  1. #1
    pplusent's Avatar
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    Engine power loss

    I have been noticing a loss in power on my 96 sl900. Top speed a year ago was 58 mph in chop, but now I am barely getting it ti 45 on glassy water. I have also been getting an occasional bog off idle. My acceleration pump has been modified and fills on return fuel pressure, so this could be a problem with fuel pressure.
    Changed out all lines and clamps but issue remained. Engine runs good but not strong and the occasional bogg.
    Any trouble shooting tip?


  2. #2
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    Put that accel pump back to the way it should be. You could be messing up all sorts of things by having it wrong. This is a time proven setup, no need to reinvent the wheel. Besides, there is no return fuel pressure after the carbs, the restrictor is in the carb fuel outlet.

  3. #3
    pplusent's Avatar
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    acc pump

    Quote Originally Posted by BryanP View Post
    Put that accel pump back to the way it should be. You could be messing up all sorts of things by having it wrong. This is a time proven setup, no need to reinvent the wheel. Besides, there is no return fuel pressure after the carbs, the restrictor is in the carb fuel outlet.
    I have three sets of carbs for this ski and none of the acc pumps work when they are stock, the stock set up is badly flawed. I have run across the acc pump problem on this site many times and this mod worked every times. This mod has worked well for three years and has zero recovery time. The well is always full of fuel no matter how many times or how quickly you hit the throttle.
    The return line normally has about 14 psi of pressure in the tank system, but for some reason it is not pressurizing this year which seems to effect the acc pump only at idle.
    Last edited by pplusent; 08-05-2014 at 11:45 AM.

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by pplusent View Post
    ...
    The return line normally has about 14 psi of pressure in the tank system, but for some reason it is not pressurizing this year which seems to effect the acc pump only at idle.
    I am not aware of any part of the carburetor fuel system that has anywhere near 14 PSI of fuel pressure, relative to ambient air barometric.

    The carburetor fuel pumps max out at something under or near 6 PSI as I recall.

    The return fuel flow to the tank beyond the fuel return flow restrictor is only pressurized by the trapped air inside the fuel tank, and that is limited to about 2-2.5 PSI positive air pressure by the pressure release venting check valve for the fuel tank.

    In the stock configuration it is not uncommon to need to prime the accelerator pumps. The typical method is to use a flat screwdriver to push the pump plunger farther than the normal range of travel, until the accelerator pump is filled with fuel and pumping properly. Once primed they should stay primed.

    If the accel pump diaphragm is failing then it will not work properly, of course.

    The accel pump should not affect top speed. Look elsewhere for the cause.

    Cylinder compression checked? Has it changed?

    Correct spark plugs installed?

  5. #5
    pplusent's Avatar
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    The return definitely holds some pressure, it would have to put a gauge on it to get the exact pressure, but its up there and the Polaris mechanic at the Polaris shop told me it was up to 14 psi. It is enough to overcome the check valve I have in the acc pump.

    When you disconnect a line when the engine is off it has pressure there, I even replaced the pressure relief valve and it still has good pressure. I could put my spare set of carbs on and try priming the pump, but I seem to recall doing that, but it was a while ago.

    Anyway, the mod works really well and its self priming. In fact it works so well that I had to go to a leaner pilot jet (58 ) and now it has neck snapping response. I found out why the occasional hesitation, I had jetted it up a while ago and had a 62 pilot jet in it. It was bogging due to being overly rich.

    I still haven't figured out the top end problem. I pulled the carbs today and found two leaking gaskets and repaired them and replaced all the lines. I will find out if that helps in about a week.

    Found two more problems yesterday when I was testing the ski. Ski keeps shutting off when at full speed, but it also failed to shut off once when lanyard was pulled and I am thinking they are the same problem. I will have to pull it apart and fix the switch or replace it with a spare.

    The other problem was the hull kept filling with water, but I filled the hull today with water and found it leaking from the waterline to the speedo. Line had a break in it, so I fix it. It just seem hard to believe that much water can come from such a little line.
    Last edited by K447; 08-05-2014 at 11:18 PM. Reason: error

  6. #6
    pplusent's Avatar
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    That jet size is a 58 not a five smiley face. Strange, I put in 58 and it keeps coming up wrong.

  7. #7
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    As far as compression, I can't seem to find my guage, but the plugs are even colored across the board. The insulators are a tan color and the rim is black but washing showing the silver, so I am assuming the comp is good.
    The engine is producing very little smoke as usual. I run a 32 to one mix as recommended by the piston manufacture, but I am going to bump it down a bit to 36 to one and see if that helps then maybe 40 (could be carbon build up). There is about 26 hours in the pistons and rings now ( pistons are forged units), so I should be able to back down on the oil now. Oh yeah, the oil injection has been disabled (don't trust it).

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by pplusent View Post
    That jet size is a 58 not a five smiley face. Strange, I put in 58 and it keeps coming up wrong.
    The forum default is to convert certain text patterns into smilies.

    The easy way around is to put a space before the )

    8) will normally convert to Name:  image.jpg
Views: 126
Size:  1.0 KB

    If Disable smilies in text is checked (I used Advanced Mode for this reply) then 8) will remain as 8)

  9. #9
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    32:1 is way too much oil.

  10. #10
    pplusent's Avatar
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    K447 after all the back and fourth on this forum on the acc pump issue your are the first that knew about priming the pump, kudos. I still like the mod, but will do if I change carbs.
    As for the oil mix, I am not sure of the spelling, but Wisco is the piston manufacture and from what they say the forged pistons need more oil. I personally don't understand that, it must be a two stroke thing because I have been using forged pistons in my 4 stroke racing engines for 3o years and the do not require any extra oiling.

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