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  1. #1

    Rejetting with Low restriction flame arrestor

    I just installed the updated airbox kit on a 1993 SL 750. As part of the upgrade kit, the High speed jets were increased from stock to 102.5 As recommended by many posters, I rebuilt the carbs, replaced the fuel pump and balance of the fuel system while I was in there. Pilot jets were not changed. As you can imagine, the sled falls on its face when you crack the throttle, but if you flutter the throttle to get past the bog, it runs strong. I opened the low speed adjusters about 3/4 turn and the hesitation went away, but now it is a bear to start - it floods. My guess is that I need to return the low speed adjuster to stock and then increase the pilot jets in size - the BIG question is by how much ? The originals are 72.5 Any advice is greatly appreciated. Thanks


  2. #2
    RLACEMAN's Avatar
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    Did the airbox update kit suggest a change in pilot jet size? & did you remove & clean the pilots? Sometimes those pilot jets are so small they build up a coating over years of use that cannot be cleaned off. Also are you using fuel with ethanol, that alone will require one or 2 upsizes. I would go to a 75 in pilot & turn screws to 1/2 turn out. I put the same airbox on my 94 slt750 & went up in pilot one size & it helped on the same low end bog, but I need to go more cause its still there.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Which update kit did you use?

    Ken at Ocean Pro recommends leaving stock jetting and only opening the high screws OUT an additional 1/2 turn when using Vortex FA's.

    Maybe try that and watch your piston wash????

  4. #4
    The update kit was a Polaris kit and did include the larger main jets. It made no mention of the pilot jets, nor did it include any. Yes, I am using 10% ethanol fuel, but I was using that before the update with no ill effects, except for the fact that the ethanol cleaned the fuel system which then clogged the carbs and started me down this road.................
    If the original pilots were 72.5, I was thinking about 77.5 As many of you know, removing these carbs is a real chore, so I really don't want to do it more than once if I can help it.
    Thanks again for your input.

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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  6. #6
    Virtually the same kit, except instead of 3 individual flame arrestors, it is a single rectangular flame arrestor. The instructions for replacing the high speed jets are the same. I neglected to mention in my original post that I am intentionally running the high speed adjusters a tad rich to avoid a potential meltdown. Despite that, the top end is really good, but as soon as you close the throttle below about half, it gets really cranky.
    Pop off is 16 PSI - which is the high end of the spec and I changed the needle valve from the original 1.5 to 2 which appears to be what the later model 750's used. Is there a way to correlate an increase in jet size to opening the adjusters by a full turn ? Thanks again

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    As far as i remember, all Polaris Mikuni carbs came stock with 2.0 needles and seats. Not 1.5's

    Did you check your pop off pressure after the new N/S combo?

    To answer your Q, I don't know.....

  8. #8
    If all Polaris came with 2.0's then mine had been tinkered with as I definitely took out 1.5"s and yes, the pop off was tested after the N/S was changed to 2.0
    I guess this is going to be a hit or miss proposition, I am going to start with 77.5 and see what happens.

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Not all Polaris, just the ones with Mikuni carbs stock. (blue Fuji engines)

    So are your jets stock size?

  10. #10
    It is a blue Fuji with Mikuni carbs. As of this writing, the high speeds are the replacements that came with the kit - 102.5 The low speeds are the originals - 72.5 To recap, if I turn the low speed adjusters out an additional 1 to 1.5 turns the hesitation goes away, it idles OK, and the boat runs strong, but, it is impossible to start. I am dumping too much fuel with the throttle closed. Put the low speed adjusters back to stock settings, it starts very easily, idles fine but there is a huge flat spot after about 1/3 throttle. If I am understanding the Mikuni manual correctly, the sequence in the carb for fuel delivery regulation is Low speed adjuster, then low speed jet, then pop off, then high speed jet and finally high speed adjuster.

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