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Thread: Top end rebuild

  1. #1

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    Top end rebuild

    Hey all-
    I'm in the middle of doing a topend rebuild. I've got my jugs back from the machine shop and am ready to reassemble, clean carbs and break in. My question pertains to the initial carb setup and break in procedure. I'm wondering, when I am starting the ski up for the first time with the new parts, should I try to setup the mixture/idle settings first before break in or break in first, then tune the idle and mixture? Also, should the base carb settings in the manual be okay for break in? Thanks for any input.

    --Justin

    edit: the ski is a 1996 700slt if needed


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    I am sure others with more experience will respond.

    Are you running pre-mixed oil=fuel, or the stock oil pump?

    If you are using the oil pump (which is OK by me), are the oil lines fairly new, or the original old hoses? You may want to replace the hose at some point, if they are old.

    What exactly is the break-in procedure you plan to use?

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Does your ski have any mods done?

    If so, the jetting will possibly need to be changed.

    How big of an oversize are the new pistons?

    If it's say .75mm OS jetting may need to be adjusted.

    Are you running premix or oil injection?

    If you're running the oil injection, add a couple ounces of oil to the gas tank during break in.
    If you're running premix, then run 32:1 gas/oil ratio.

    If you're basicly stock. Just set the carbs to factory specs.

    Set to factory specs while doing break in. After that, you'll need to make your changes for the mods done. (watch piston wash)

  4. #4

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    Thanks for the replies. The ski is stock, oil injection is being used so I'll add some oil to the gas for break in. I got the jugs bored out .5 mil oversized. Other than that, no mods. The break in procedure I was planning to use is the one described here: http://www.***********.com/showthread.php?t=18

    If there is a better one that you know of, let me know. Everything else I found when I did a search said basically the same thing as that post. Thanks for the help.

    --Justin

    the link didn't work so here's the quoted instructions:

    For jet-skis that utilize an oil and fuel pre-mix system, the oil to fuel ratio should be enriched to a ratio of 32:1 for the first ten gallons of gas that is run. If the jet-ski is equipped with an oil injection system, then a 50:1 ratio of fuel to oil is recommended to be run through for the first ten gallons.

    Upon initial startup, let the jet-ski idle for ten minutes to allow the engine to warm up and to allow oil to permeate internal gaskets and engine components. During the initial ten gallons of fuel being run through the jet-ski, the jet-ski should never be operated at full throttle. Doing so can potential cause damage to piston rings, pistons, and engine cylinder walls.

    Begin cycling the throttle from idle up to 20% capacity and back down to idle for a full half hour while riding. Bring the jet-ski back and shut off the engine to allow it cool for at least half an hour.

    Restart the jet-ski and bring the throttle to 50% capacity for a full half hour while riding. Bring the jet-ski back and shut off the engine to allow it to cool for at least half an hour.

    Restart the jet-ski and bring the throttle to 90% capacity for a full half hour while riding. Bring the jet-ski back and shut off the engine to allow it to cool for at least half and hour. Repeat the process of riding the jet-ski at 90% capacity for half an hour and letting it cool for half an hour until all ten gallons of fuel are gone.

    Never hold the throttle at a static level for more than a few seconds – it is important to cycle the throttle as much as possible during the engine break in period.

    After the first ten gallons have been depleted, replace the spark plugs in the jet-ski with new plugs. Restart the jet ski and operate it as you normally would for the entire second tank of gas without bringing the throttle to 100% capacity for more than five seconds at a time.

    Once the second tank of gas has been depleted, your jet-ski is broken in and you may ride it to its capacity.

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Throughout the break-in process, you want to continually vary the throttle position,within reason.

    The MotoMan method is interesting, and does make sense to me. Other than the complete warm up before starting break-in, I am not clear whether it fully applies to 2-stroke engines.

    It is unclear to me whether the initial roughness of the honing is a major factor in how rapidly you can work up to full throttle operation.

    Here is a variation of the gradual procedure you listed.

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