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  1. #1
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Adjusting pop-off pressure, and is top or bottom end of range 'better'

    OK, got the first carb buttoned back up after putting in new parts. Pop-off is 19 PSI, book wants it to be 20-24.

    Since I have to adjust it anyway, which end of the range is 'better' or aim for the middle? Or just all the same is the only thing that matters?

    John told me to just reuse the old grey springs, everyone agrees?

    Bending needle side of rod UP causes a DECREASE in pop-off pressure and DOWN causes an INCREASE, right?

    I may just try the new spring and see if that fixes it.


  2. #2
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    Use the spring that was in the carbs. If you use the right needle and seat, and correct spring, you should be fine. I don't think you will have any problems at 19 PSI. There can be variances in gauges as well. Read the Mikuni tuning guide to learn what effect popoff has on running. Its in the tech tips section. Its a really good read.

  3. #3
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    Yep, what he said ^^^^

  4. #4
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    So I shouldn't bother tweaking the arm to get 20-24?

    I tried the black spring and was able to get 22. Will the black spring cause other issues?

    This is really just to prevent dumping fuel to the jets until there is more vacuum in the carb, right?

    OK, so the low speed jet is stock, and I am leaving that one alone, the manual notes 'if the low speed jet is slightly too small, you can compensate with slightly less pop-off pressure' I think I am going to go that route and put the grey spring back in and tune them all to 19PSI. This will effectively act like a larger low-speed jet.

    I am putting in new high speed jets (115 vs the stock 110) in the hopes of being able to run lower octane or even the newer 15% ethanol without going lean.

    Comments?

  5. #5
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    I would never run any percent of ethanol. (If possible) #1, The alcohol absorbs water badly. #2, On 2 strokes the fuel and oil lube the crank bearings, and alcohal dulutes fuel's lubricating value.

  6. #6
    BlueFishCrisis's Avatar
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    More fuel doesn't make up for bad fuel. Is the only reason you are changing jetting is because of octane??

  7. #7
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Not entirely.

    My two running SLT780s both run a bit more lean than I would like, even on premium, and the high-speed screws are at or near 2 turns out. I have read many posts saying this really indicates you need bigger jets.

    The only places around here that sell ethanol free gas are the marinas, and their prices are just ridiculous. So mid-grade or premium, both with ethanol, are my only feasible choices.

    So between both of those, the bigger jets seem like a good idea.

    Now I am hearing rumblings we will be going to 15% ethanol...which again won't help any.

    I'd rather be a bit rich than a bit lean.

  8. #8
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    I wouldn't mess with popoff, and just change the low jets as needed. Run the black spring, I think its the right one. 2 turns out is ok I think. They say 3 turns is the max before it doesn't have an effect any more.

  9. #9
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    I did some math, and I am leaning back towards just buying the better gas now. It comes out to about $20 per tank diff for regular-ethanol vs the non-ethanol 92 I can get at the nearest marina. Thinking that is not worth the effort of carrying cans around and the risks to the marine gear.

    I'll still put the 110s in the SLX, but I am going to switch to the ethanol free 92 octane for a while and see what the wash pattern does.

  10. #10
    ujustlost's Avatar
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    Good call , ethanol free is the only way to go

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