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  1. #1
    rustyrider's Avatar
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    ski NOOB- sl750 help

    hey guys. I just bought a 96 sl780 2 days ago off of craigslist for 500 bucks! this is my first ski. The hull is in awesome shape and the ski was really well taken care of. The only problem was that it burnt a whole through the 3rd piston. The PO gave me a new jug, piston and head which was pretty awesome and i finished putting it in yesterday. I started it up and got it going. starts up pretty easy now but it has a high idle and im scared to run it for a long time before i know everything is in good shape. Im guessing the motor was running lean and thats why there was a hole in the piston. It also is idleing around 4300rpm?? I dont know where to start because there could be so many things causing it to lean. One thing i noticed is that when i loosened the gas cap it made a big hiss so im guessing the vent line is clogged and it might be starving the motor.

    Other than that what else should i look for? how do i know the old pump is working correctly? What should it idle at? what should it sound like? what other precautions should i take? I was thinking about premixing. where do i get a "blockoff plate"??

    Thanks, Justin


  2. #2
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Welcome to the Hulk Justin!
    They didn't make a 750 in 96. If it's a 96 model it may be a 780. If it's a 750 they made them through 95.
    If you have a single outlet fuel pump, most here will agree that you need to upgrade to a triple outlet pump. The single was barely able to provide enough fuel when it's in great shape, and as it gets worn will starve the engine of fuel. If your ski has the grey Tempo brand fuel lines, the carbs are probably gunked up w/ a greenish goo. The goo comes from the fuel lines as they break down internally. You need to replace all the lines including the ones in the tank if present. If you have the 750, it will also have a restrictor in the return line from the carbs to the tanks. The restrictor is near the carb and may be held in place by ties. You will need to locate it and reinstall it in the new return line. You need to go through the carbs and clean the internal strainers, replace or clean( depending on the type you have) the external fuel filter.
    The hiss you heard when you opened the fuel cap, was it in a vacuum or under pressure? It could be under pressure of up to 1.5 psi or a slight vacuum. When you replace the lines, you can use air to blow through the check valves for the tank.
    the check valves are items 13 and 10 in the diagram. Item 14 is the restrictor if you have the 750. Let us know what you have.
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  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by rustyrider View Post
    ...'96 sl750 ...my first ski...

    The only problem was that it burnt a whole through the 3rd piston. The PO gave me a new jug, piston and head which was pretty awesome and i finished putting it in yesterday.

    I started it up and got it going. starts up pretty easy now but it has a high idle and im scared to run it for a long time before i know everything is in good shape.

    ...It also is idling around 4300rpm??
    I don't know where to start because there could be so many things causing it to lean. One thing I noticed is that when i loosened the gas cap it made a big hiss so I'm guessing the vent line is clogged and it might be starving the motor.

    ...What should it idle at? what should it sound like? what other precautions should i take?
    I was thinking about premixing. where do i get a "blockoff plate"??

    Thanks, Justin
    Welcome to the Hulk!

    Click here to find Polaris Service Manuals and other useful info. The service manual outlines how to check and set the idle.

    This recent thread discusses a similar situation with another new member.

    When you installed the 'new' cylinder and piston, was it actually brand spanking new from Polaris, or a refurbished cylinder?

    Were the new piston and piston rings checked for proper fit and gap clearances in the cylinder?

    Once you get the fuel system up to par, and the idle issue sorted, there is a break-in procedure to follow to ensure good seating of the new piston rings in the new cylinder.

    The normal recommendation is to replace 100% of the old fuel line, including any that is inside the fuel tank. Be sure not to lose the brass fuel restrictor, if yours has one, that fits inside the old return fuel line, near the carbs.

    Then install the triple outlet fuel pump (which was the actually standard fuel pump on the 780cc engine). John Zigler is one source for the triple outlet fuel pumps.

    Confirm that the fuel tank vent check valves are working properly. Service Manual shows how to do this.

    Pre-mixing - the Fuji/Polaris oil pumps are actually quite reliable. Many owners continue to run with the original oil pumps, without trouble. Retaining the oil pump means you don't have to deal with, or remember, to pre-mix the oil with the fuel.

    You should replace all the old oil lines, install a new oil filter, and bleed the air out of the new hoses.

    Since you are breaking in a new cylinder, you should also follow the service manual recommendation for adding 2-stroke oil to the fuel tank during break-in.

    Some owners feel that the oil pump system is a liability. As long as you can be certain that every tank will be properly pre-mixed with oil, and no other riders will forget and re-fuel without oil, then pre-mix is an option.

    Some owners make up their own oil pump block off plate, but they can also be purchased, from places like Watcon. If you remove the pump, be sure to remove all the parts from inside the engine.

    One advantage of the variable rate oil pump system (the oil pump has a linkage to the throttle on the carbs) is that it reduces oil consumption by about 50% compared to pre-mixing. At high RPM WOT, you get full oil flow. At low RPM, the pump reduces oil flow, since the engine doesn't need as much oil.

    The oil pump also has a fail safe feature. If the variable rate linkage disconnects, the spring loaded arm falls back beyond the normal idle position, and the pump goes to 100% oil flow mode. This protects the engine from oil starvation.
    Last edited by K447; 04-06-2009 at 07:41 PM.

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk Rusty.

    It seems you've been reading up on here, that's good.

    If you've been on here recntly, you'll see that 2 new guys have asked the same thing this week alone. Please read through their threads for some answers.

    But as a general reply, this should help you. http://www.greenhulk.net/forums/showthread.php?t=82682

  5. #5
    rustyrider's Avatar
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    thanks for the replies guys! It is a 96 sl780 sorry i call it a 750 alot for some reason (maybe cause og the gsxr ). It looks like it has a 5 hose fuel pump so i guess thats probably not the problem. I cant tell if the hissing is pressure or vacuum but it is pretty loud and sometimes lasts almost 3 seconds and seems like its more than it should be. I just found out that the bottom of the front storage compartment comes out which is pretty handy. i found the vent, return and send lines on the tank and followed the vent up to the nozzle thing on the outside of the ski. how would i check to see if the vent is clogged and how should i fix it if it is? The fuel lines look and feel like they are in decent shape(still soft and flexible). is there anything i could put in the tank like a fuel system cleaner or anything?

  6. #6
    rustyrider's Avatar
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    oh yeah i forgot. the piston and jug came from another 96 sl780 the guy i got it from had. they looked to be in good shape.

    I blew through the vent line at the tank side and could not blow through it. I also blew through the vent side towards tank side of the line and couldnt blow(check valve i guess). Im wondering if the vent check valve is stuck closed and i could fix it by blowing through it with a compressor??

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by rustyrider View Post
    ...96 SL780
    ...It looks like it has a 5 hose fuel pump so i guess that's probably not the problem.
    I cant tell if the hissing is pressure or vacuum but it is pretty loud and sometimes lasts almost 3 seconds and seems like its more than it should be.
    ...I found the vent, return and send lines on the tank and followed the vent up to the nozzle thing on the outside of the ski.
    How would i check to see if the vent is clogged and how should i fix it if it is?

    The fuel lines look and feel like they are in decent shape (still soft and flexible).
    Is there anything i could put in the tank like a fuel system cleaner or anything?
    Quote Originally Posted by rustyrider View Post
    ...I blew through the vent line at the tank side and could not blow through it. I also blew through the vent side towards tank side of the line and couldnt blow(check valve i guess).

    I'm wondering if the vent check valve is stuck closed and i could fix it by blowing through it with a compressor??
    Quote Originally Posted by K447 View Post
    ...Click here to find Polaris Service Manuals and other useful info. The service manual outlines how to check and set the idle.

    ...Confirm that the fuel tank vent check valves are working properly. Service Manual shows how to do this...
    If the check valves are sticking, I would suggest replacement. They are not expensive, and you don't want fuel tank pressure to cause a problem.

    One member had his entire engine filled with gasoline because a tank vent wasn't working, and he forgot to shut off the fuel switch.

  8. #8
    rustyrider's Avatar
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    i dont think its a tank pressure issue now because i ran it with the gas cap off and it did the same thing. WHen i choked it the rpms dropped again and it idled slow. with the choke off it idles around 3000!

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by rustyrider View Post
    I don't think its a tank pressure issue now because i ran it with the gas cap off and it did the same thing..
    Do not assume the machine only has one problem.

    The fuel tank vents can be stuck, and you can have an issue with engine air leak or carb settings.

  10. #10
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Quote Originally Posted by rustyrider View Post
    The fuel lines look and feel like they are in decent shape(still soft and flexible). is there anything i could put in the tank like a fuel system cleaner or anything?
    They may feel good and look good on the out side, but if they are Grey Tempo brand lines, they have to go! Here is a pic of a good looking line thats still soft and pliable, but look on the inside. That crap will clog your carbs bro.
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