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  1. #1

    Polaris SLX 780 Lean or not?

    Ok as advised, i have started a new thread. I will attempt to outline everything I have done thus far to correct what I believe was a lean condition likely do to a 6 year sit in the garage. The first top end rebuild was a failure and i have been paranoid Id crater again. Today I broke down and removed the heads and after looking at the pics, I fear my paranoid ass may have got the best of me but I will let the experts weigh in. My fear was that the mag cylinder was still lean as I could not increase the size of the wash. These pics were run doing plug chops and the settings were a half turn over factory recommended (cant recall each as i write this).

    1.) top end rebuild 2x
    2.) New OEM gaskets
    3.) cleaned fuel tank to like new condition
    4.) 92 octane gas added
    5.) carburators cleaned three times
    6.) new needles and seats and diaphrams OEM
    7.) performed pop off pressure check on carb rack (acceptable)
    8.) Rebuilt triple out fuel pump OEM parts
    9.) Performed leak down test (held well over 20 minutes)
    10.) Replaced all fuel lines and pulse lines. Lines cut to same length as original however bypassed the pect cock valve.
    11.) new orings on carb adjusters.
    12.) checked all check valves in lines.
    13.) verified oil pump delivery. Created bubble in each line and watched it move. Also found oil inside cavity on carbs.
    14.) made certain all carb ports were clear including inline attached orifice. Shot carb cleaner thru it till it shot across the room.
    15.) attempted twice to check fuel pressure between center and mag but failed as the rental ga didnt have small enough increments. Just bout a jegs ga today that should do the trick. 1.5 at idle and 4+ at WOT ???
    15.) Damn...seems like there was more but Im thinking that about sums it up quickly.

    Judging from the pics and my untrained eye, it doesnt look like I have a lean issue. I would still like to see more wash on mag since the adjuster is open a half turn over factory set but wonder if the center having so much wash might be hogging fuel ( my attempt at logic please dont laugh).

    Anyway -Whats it look like to yall? Should I reinstall and start leaning out the other two cylinders? Ran real rough with current carb adjustments. loads up at low speed. WOT cleans up. Prolly to rich right?
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    Last edited by Lockout; 05-30-2010 at 07:05 PM. Reason: PICS DIDNT ADD

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Your MAG isn't BAD. I would like to see a little more wash to be safe. Maybe go up 1 jet size if you're at your max turns out with that one. (2 1/2 turns out is max)

    CEN head is junk, replace that. Wash is way rich. Give that 1/4 turn IN and recheck later. (safer to be rich than lean)

    PTO isn't the prefered wash at every port, but it's getting good fuel supply. (should be fine leaving it as is)

    Verfiy your fuel pressure readings at WOT. (4-6 psi) If that tests out OK, then up the MAG jet 1 size.

    To answer your previous question, the head gaskets are situated with the "sharks fin" directly under the cooling rail, and the 78 being legible. (not backwards/upside-down)

  3. #3
    Already ordered a new head for the center. As for increasing jet size on Mag. I will do but dont understand why a stock machine should need a jet increase? Have u ever seen this need before on a stock machine?

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    See if you can get another head from one of the guys parting out a 780 in the classifieds or from John Zigler. It will be much cheaper than ordering one.

    First, do that fuel pressure test and see what you get.

    I don't know why the MAG would need more fuel than what came stock, could be a small air leak, slight water restriction, higher compression, tighter squish, advanced timing, hotter spark plug, anything.....

    All I know is that cyl needs a little more fuel to make you happy. Beating your head against the wall trying to find the minute cause just isn't worth it. Give that cyl the fuel it needs and enjoy your ski for the summer.

  5. #5
    I heard that. Sounds good. I will get a size larger jet on order today. As for the head. I got a used one coming from a local guy for 18 bucks delivered. Cant beat that with a stick. In fact, i bought two cause I know the other ski is going to need new ones as well. I will give a status on fuel pressure when i get it back on the water.

  6. #6
    Am I correct that the nextmain jet size up is a #112 ? Stock would be #110? Any suggestion on a place to purchase?

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    They go in increments of 2.5, so yes a 112.5 would be 1 size up.

    Got any powersport places near you? (ATV, PWC, dirtbikes, etc..) They may have jets that work. Take 1 with you to match up. That will prevent you from having to pay more in shipping than the cost of the jet.

    If you don't, has fast shipping. Would be to you in 2-3 days.

  8. #8 112.5 main jet, new carb base gaskets...reinstalled. Carbs set at M 1 1/2 C 7/8 P 1 1/2. Does this sound ok to start out? Gonna throw the fuel pressure in between the center and Mag cylinders and see what happens.

  9. #9
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
    Join Date
    Aug 2006
    Pittsfield, MA
    Wow, I better check my SLX. I'm at the factory settings I think and the cylinders are all 1.5mm over sized on the SBT engine. Probably lean all around. Can't hurt to check

  10. #10
    Plrs X45's Avatar
    Join Date
    Sep 2006
    Joliet, Il
    I actually ran into this problem when I owned my 780 SLX. I had the engine rebuilt by a person who builds snowmobile engines and he said replace the fuel pump and go up one jet size and that the stock jets were barely the minimum. I then had the manifold extrude honed, took 7 thousandths off the heads and put it back together. NEVER had another problem and it still runs great today (see it at the river every month).

    I hope you solve your issues.

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