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  1. #1

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    Switching SL750 air box to SL780 air box

    So I was able to pickup a used SL780 air box off of eBay to replace the stock one with all the cracks... I think it had only two remaining useable screw holes!

    Im now wondering where to mount the triple-outlet fuel pump since the 780 air box doesn't have the holes to mount the fuel pump plate like the 750 does. Should I reuse the plate and screw it into the edge of the small hull bulkhead just below it?

    What have others done that have done this upgrade or added aftermarket flame arrestors?


  2. #2
    BlueFishCrisis's Avatar
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    Mount it to one of the ribs on the hull....

  3. #3

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    Well the pump was easy enough to mount on the bulkhead rib using the original mounting plate – thanks BFC. The problem came when I went to install the 780 air box. The inside edge of it interferes with the cylinder and heads. Im guessing either the 780 cylinders/heads aren't as wide as the 750's (unlikely), or the 780 intake manifold sets the carbs just a little bit further out than the 750.

    My next question now is, will a 780 intake manifold fit and work on a 750, setting the carbs out just far enough so I can use the 780 air box? Or am I destined to seal and caulk the everlivin' crap out of my original, and thoroughly cracked air box cover?

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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  5. #5
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    Just put in a set of reed spacers........It will help with reed longevity and maybe a little with performance. That will solve your clearance issue. Where are your oil injection nipples? Are they on the manifold out on the stock 750 air box. You may need to accomodate for those too.

  6. #6
    BlueFishCrisis's Avatar
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    Does yours look like this?


    Click image for larger version. 

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  7. #7

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    K447: a little search does wonders! So it's obvious that the air box shouldn't just drop on without serious modifications.

    BryanP: I liked the idea of reed spacers, but I did a quick search and couldn't find anything used, and new from Boysen would cost about as much a new set of OP Vortex FA's. Oil nipples are not a problem as I'm now running pre-mix.

    BlueFishCrisis: Now that's an idea! I could just remove the cylinder side section of the air cover to make it fit. I'm guessing the 780 element isn't much different construction-wise from the OP flame arrestors, and leaving them exposed there wouldn't be much of an issue, correct? Well other than a bit of carb tuning I guess. I've always wondered about engines that had more exposed flame arrestor elements, and if they're more susceptible to water ingestion. I ride quite almost exclusively in Lake Huron and won't hesitate to head out in up to 6' swells on waves day. I often take on a bit of water with breaking waves and occaisionally flip it. Am I running more of a risk modifying and switching to this air box over the OEM cover with rubber elbow?

  8. #8
    BlueFishCrisis's Avatar
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    Quote Originally Posted by SeaBee63 View Post
    Am I running more of a risk modifying and switching to this air box over the OEM cover with rubber elbow?
    I think the benefits outweigh the risks.......

    I have a set of reed spacers for you. You'll need to dig up the hardware though......

  9. #9
    RLACEMAN's Avatar
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    The air box should drop on without modifications, I have one on my SLT, but I do have reed spacers on it. There was Polaris update using this airbox on 750's. The 780 airbox is slightly offset & needs to be put on with the lettering on top being read by standing on the RIGHT side of the ski, it may be snug without reed spacers, take the cover & put the air element in it, then turn over holding the element in with your fingers, then put the cover on, there may be contact between the cover & cylinders, if so you can force it in or remove some material from the cover, (probably less than an inch) with a jig saw. Also don't forget to adjust your high speed mixture screws accordingly, they will need to be turned out. The original setting were alot different between the cylinders & varied between 94 or 95, Start out at least 1 1/2 turns out from seated position on each carb. I ended up with Mag 1 1/2-Center 1 1/4- PTO 1 1/2, low speed screws needed to be turned out another 1/8 to 1/4 turn too.

  10. #10
    rpa101's Avatar
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    When I got the up dated filter years ago it came with longer bolts and 3/4" spacers with oil inj. Lines I might still have them and the bolts if it will help let me know and I will look for them you can have them

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