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  1. #1

    Cool SL 750 - Lean or Not Lean how do you know

    Hello all,

    Just finished a complete overhaul of a 95 SL750 with the old common hole in center piston. Did everything i could find (read about) in the forums

    -total tear down, clean / inspect, gasket replace, step by step to the polaris manual (including new crank seals)
    -upgrade to 3 output fuel pump
    -All new fuel lines (including inspection of return line restrictor), filter, checked all vents, pressures etc
    -Eliminated fuel shut off valve
    -Remove, clean and inspect fuel tank pickup
    -New (used) oil pump, all lines, filter, bleed and visual check for pumping
    -Remove, clean and reset carbs to factory settings
    -timing check
    -new plugs (BPR7ES) as per manual

    Likely did more but then this but its all I can remember for now.

    My question is this: It seems to me that it's still running lean in the center and Mag cyclinders. After running gently for about 10 minutes the new plugs are dry and grey white looking? Turned the high speed carb adjusters up 1/2 turn (for now) to be safe and after another very brief run they look a little 'wetter'. How does one really know if they have everything correct and its not going to burn up again (trick's of the trade is what I need now).

    Thanks allot guy's for any more insight!


  2. #2
    Moderator beerdart's Avatar
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    Piston Wash is the most accurate. Plug chops should get you close.

    Check out this section.
    http://www.greenhulk.net/forums/showthread.php?t=15473

  3. #3
    Hi, Thanks for post (re reading all the info you linked me to).

    With piston wash is it not hard to tell (looking down the plug hole) as to really tell won't you have to remove the head?

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by killer View Post
    ...With piston wash is it not hard to tell (looking down the plug hole) as to really tell won't you have to remove the head?
    Use a really slim, bright light. There are a number of these 'inspection lights' sold by automotive supply places, and some of the new slim LED flashlights can also work.

    Just don't drop the light inside!

    Rotate the drive shaft coupler to love one piston to the bottom of its travel, and have a look through the spark plug hole. Best done in a dim or dark place (through a big towel over your head and the engine), or at night.

    Inspect, make notes, then rotate the next piston down, check that one, and so on.

    To take pictures of the piston wash, you really do need to remove the cylinder heads, unless you have some very fancy photography gear.

  5. #5
    Moderator beerdart's Avatar
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    Yes it is hard to tell with the heads on Get a small snake lite and stick it thru the spark plug hole. Some use a borescope.

  6. #6
    Well I had a pen light and did as suggested, the center and Mag cylinders (although oil / wet on top) have cleaner (near shinny) areas near the exhaust port side. The PTO is much better. I don't get it, I have done everything I found in the forums. I guess I will just put the carb settings back to factory and then perhaps put the high speed settings 1/4 turn richer and try again?

  7. #7
    Moderator beerdart's Avatar
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    You want shinny near the ports. You can also install BPR8ES plugs.

  8. #8
    gorilla03's Avatar
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    did you do a leak down test? you could be getting extra air inside the crankcase that could be causing a lean condition....

  9. #9
    Actually .. After all this work no, not a true leak down. I will do it before moving on.

    I know when I first put it all back together I had fuel / pressure etc leaking from the exhaust side of the motor and then discovered I forgot to put three small bolts back into the lower 1/2 of the crank case (item 14 & 15 if you have the polaris manual handy pg 4/96 case exploded view 94/95 750's). I am not sure what they were for in the first place as they would close up holes in what would seam to be an empty chamber down the exhaust side of each cylinder jug down into the both the top and bottom of the crank case. When I looked at the 1993 model year it looks like this use to be for additional water cooling jacket system? Perhaps in my case air / gas should not have been getting into this area in the first place, like maybe I did not use enough sealant on the two crank case surfaces when I put it back together?



  10. #10
    gorilla03's Avatar
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    Quote Originally Posted by killer View Post
    Actually .. After all this work no, not a true leak down. I will do it before moving on.

    I know when I first put it all back together I had fuel / pressure etc leaking from the exhaust side of the motor and then discovered I forgot to put three small bolts back into the lower 1/2 of the crank case (item 14 & 15 if you have the polaris manual handy pg 4/96 case exploded view 94/95 750's). I am not sure what they were for in the first place as they would close up holes in what would seam to be an empty chamber down the exhaust side of each cylinder jug down into the both the top and bottom of the crank case. When I looked at the 1993 model year it looks like this use to be for additional water cooling jacket system? Perhaps in my case air / gas should not have been getting into this area in the first place, like maybe I did not use enough sealant on the two crank case surfaces when I put it back together?

    I believe the cooling system changed on the 94's...even a small pin hole size leak could cause a very lean condition, check that out and let us know what you come up with

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