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Not another jetting question!

Discussion in 'XJ Technical Chat' started by Neil Abbott, Jul 5, 2017.

  1. Neil Abbott

    Neil Abbott New Member

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    Due to a failure (rust/rot) of the factory mufflers and the inability to find any for sale at the time I decided to install a MAC 4-1 system. Based off of other threads I decided to jump straight to a 126 main and keep the factory 40 idle jets. While performing plug chops the top end is still producing a plug with no color on the ceramic. Based off of experience what kind of change in plug color should I expect to see from going up one size jet as opposed to two sizes? Is the change from one size to the next a minor amount or is it very substantial?
     
    Neil Abbott, Jul 5, 2017
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  2. Jetfixer

    Jetfixer Well-Known Member

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    Have you adjusted mixture screws? A larger jet has a big effect , but the mixture screws should be set at 2.5 turns out and go up .5 turns and check plug color this is other part of equation. I have a stock airbox and a Mac 4 into 2 exhaust , stock Main jet is a 120 I put a 124 in my mixture screws are all set at 3 turns out my plugs are all a brown color . This works on my bike at least :)
     
    Jetfixer, Jul 5, 2017
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  3. Neil Abbott

    Neil Abbott New Member

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    I have attempted adjusting the mixture screws but am becoming too rich at idle by the time I start enriching the top end.
     
    Neil Abbott, Jul 5, 2017
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  4. Jetfixer

    Jetfixer Well-Known Member

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    Turn all the way in soft set bac out 2.5 turns see how it runs there...ride a few miles pull plugs see what color tip is if it is lean back out a quarter turn recheck ...you may have to go down to a 124 jet if you cant get it to not run rich.
     
    Jetfixer, Jul 5, 2017
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