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  1. #1

    Exclamation 1994 Polaris SL 750 Hole in Piston

    I know I have seen this topic a few times here, but I wanna point out something important that is specificly to my ski.

    I bought this thing running, ready for the water. I had a blast, was so freaking fun, it went 50mph clocked on my bro's WaveRunner(my display wasn't showing anything). It has a good bit of aftermarket stuff on it including reefs, intakes, and now I know it has SBT .50 pistons on it.

    Well it ran fine for about 2 hours of a good bit of WOT and some just cruising. Then it would be hard to keep running(idle) and would only hit about 15mph on WOT. When I got home, spark was good, so I check compression and the MAG(#1) had 0 compression. broke down the engine and found a hole in the cylinder and wonder. Did my homework and found it's very common on this ski. So I realize I need to upgrade my fuel pump to a 3 outlet to prevent this from happening again. I ran across how the 3 outlet pump is hooked up and just looked at my ski and noticed that the ski had a homemade 3 outlet, using the stock 1 outlet fuel pump. Somone slpit the hoses between the carbs and jumped into the fuel pump outlet. I got a pic to show you how it looks.

    But my real question lies here. What was done to this ski was obviously trying to NOT run the MAG too lean. I need to know if I get the 3 outlet pump will prevent it form happening again, and what was done with this ski was it halping or making it worse? or was the old pump just finally dying out? Please give me some help and tips on keeping this thing running without blowing another $95 piston in the trash.

    So my plans are to:

    Order/replace: MAG piston(SBT 0.50) and a 3 outlet fuel pump

    precedure: install the 2, adjust the carbs and hope for the best.

    Oh yeah and with the display not wokring what is something I can check first? Also the trim would not adjust it was stuck all the way up, what are some things that make these electronics go bad?
    Last edited by stormdlp; 06-22-2008 at 04:12 PM. Reason: forgot something

  2. #2
    As for the mfd and trim......have you opened up the electronics box and checked for blown fuses? I have a slx 780 and had the same thing hapen to me, turned out to be a blown fuse I would check this first...

  3. #3
    ok, I'll locate and check the fuses tonight, didn't know it was as easy as a car in the electronics area, makes sense.

  4. #4
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    Hey storm Welcome to the hulk..

    The way your fuel lines are routed was a Polaris SB to try and help the fuel problem. Over time the pump gets weak and flows less fuel. I like to upgrade to the larger three outlet pump from a stock 780.

  5. #5
    You've had in the past that this has "solved" the problem? as long as all the carbs and such check out, my dad is a 2-stroke expert, so we only can think we need the 3 outlet pump.

    This is just the same, correct?

    it's not a bad price, we don't need instructions nor hoses or lines.

  6. #6
    Any tips on keeping this thing running and not doing what it did again!?

  7. #7
    seaobin's Avatar
    Join Date
    Jun 2007
    Raleigh, North Carolina, United States
    check crank index

  8. #8
    1994 SL 750 - Hole in Piston #1(MAG) Fix.

    Ok guys, I want EVERYONE on this forum to read this, because almost ALL the other threads on this topic never have an ending.

    So far:

    -Boiught a new piston and installed it(make sure the same as others)
    -Thriple Outlet Fuel pump
    -cleaned out fuel selecter switch
    -double check restrictor is in return fuel line
    -double check fuel lines from tank(inside) to fuel pump
    -only new fuel lines I did were leaving the fuel pump
    -new fuel filter(I got a mower one from wal-mart)
    -after the fix I think my bilge pump went out(got an aftermarket one you just mount at the bottom of your hull with an on/off switch, works GREAT!)
    -replaced the fuse(only one I could find) in the electric box thing, and it fixed the MFD.

    ALL of these things got my ski back on the water and kicking butt man, I LOVE IT! The MFD says 55mph, but It can't be any over 50 I believe.

    Things to do now:
    -block off fuel pump and run premix
    -take out and tear down trim motor and see if it's dead or salvagable, if not, get a replacement.

    I pulled my friend on a tube with the MFD saying 45mph, this thing is a blast!

    Thanks to everyone who contributed help info, and I will keep in touch with any updates on maintaining this beast.

    here's some pics for the heck of it.

    As you can see I got pics of before and after the decal removal.
    I think it looks beter without the faded blue and reds, and that throttle lever is just a bicycle brake, for my plastic thumb one broke, this one worked nearly perfect.

    Thanks again, you guys Rock!

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    Quote Originally Posted by stormdlp View Post
    ...almost ALL the other threads on this topic never have an ending.
    Well, not enough threads here have a proper conclusion, I would tend to agree.
    -Triple Outlet Fuel pump
    Things to do now:
    -block off fuel pump and run premix
    Leave the fuel pump in, it helps the engine run better.

    As long as the oil lines and oil filter are in good shape, the oil pump itself is probably OK to keep operational.
    Simplifies fueling...

    -take out and tear down trim motor and see if it's dead or salvageable, if not, get a replacement...
    Not a big deal, but you might consider mounting the fuel pump lower on the motor, so the fuel from the tank flows more downhill towards the pump.

    But do keep the fuel pump, and the pulse line, above the pulse fitting on the crank case, so fluids from the crank case cannot pool in the pulse line or the pump.

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Welcome to the Hulk storm.

    The fuel pump may have something to do with your holed piston. So I'd upgrade it for sure. John Zigler sells the Mikuni triple outlet for around $26 if you PM him.

    Now this may not totally solve your problem as there are other factors involved with running lean.

    1. you may have an air leak (leak down test will tell you right away)
    2. the crank index may be out (too advanced can do it)
    3. wrong spark plug heat range (BPR8ES is recommended over the 7)
    4. Fuel hoses, filters, carb filters, or petcock obstructions (all common)
    5. air leaking into fuel hoses (old cracked hoses or clamps loosened up)
    6. weak pulse signal to fuel pump
    7. carb needle not opening all the way allowing fuel flow
    8. too small of jets used
    9. adjustments on carbs not made for you added .5mm oversized pistons

    So, to say the fuel pump alone will solve your problem is a foolish statement to make. You have many things to look into before this happens again.

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