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  1. #1

    Join Date
    May 2010
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    Question about lean and rich.

    OK guys what is lean and what is rich?

    Does lean mean is black in the head of piston and rich means all white?
    or the opposite? Also if it is to white do i open more the gas or close it more?

    and what is lower screw for and high screw for?
    lower means air? and high means gas? help please.

    it is a 1996 polaris slx 780


  2. #2
    Canadian Beaver Inspector jkindt's Avatar
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    Sep 2009
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    Lethbridge, AB, Canada
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    Click on THIS LINK, then read every single thing on that page. Click on every link there and read every article. It will answer all the questions that you have been asking.

  3. #3
    bowsniper's Avatar
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    lean is when the engine is getting very little fuel in the cylinders while firing. it makes for a high tempertures in the cylinder and can melt pistons, put holes right thru them or make the pistons stick to the cylinder walls.


    Rich is the opposite of that. The clyinder has way too much fuel going into the cylinder and doesnt burn completly causing lack of power, incomplete burning of the fuel(wasting unburned fuel) and will actually wash the piston clean.


    Whats good? Somewhere in between. All black pistons on the top are considered lean. clean looking pistons half or more are way too rich..

    What your looking for (depending on others opinions, not just mine) are thumbnail spots of washed areas near the intake ports and transfer ports..

    Getting a good "wash" on the pistons can take about 15 to 60 mins to start to develop.

    You can use a small flashlight down the bores to inspect wash. Or if you want to get fancy with it. you could buy a boroscope or a ear doctors tool that looks into the ear.. they both have lil lights in them.

    Or just pull the heads(providing you have new gaskets for it,some people reuse them if there good still) and take pictures of what ya got, and the guys and gals here can evaluate what you have going on..

    Look in the search function on the main page and look up piston wash,, theres a lot on the subject here already. but thats it in a nutshell.

    What you really want is thumb nail size clean spots and a chocolate brown look to the piston. then your spot on!.

    Hope this helps you understand a little about it.

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