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Calculating shim size

Discussion in 'XJ Technical Chat' started by Daniel Scott Merrill, Sep 3, 2018.

  1. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Hello all I'm new to the XJ game and am in the process of getting my 1982 xj750 maxim back up and running. Recently the bile only ran on choke and checked the carbs and they were fine. Either way I'm doing valves next and was curious as to how you calculate the shim size you need after measuring and checking the shim number.
     
  2. Toomanybikes

    Toomanybikes Well-Known Member

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    So if the bike only runs on choke, carbs are not fine. Pilot jets and/or float height is too low or mixture screws are clogged
    ( small brass or aluminum plug on US models needs to be removed).

    If it’s too tight then a smaller size will be needed.
    Eg. 275 is in there and clearance is .0012 then 270 shim . If clearance is .0006 then 265 shim. 275 shim is 2.75 mm thick. It’s just math to get to 0015-0020 clearance.
    I’m guessing you don’t have a manual?
     

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    Last edited: Sep 3, 2018
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  3. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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  4. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    You've got too many zeros to the right of the decimal (I'm the typo King around here)

    intake clearances are 0.11 - 0.15 mm
    exhaust clearances are 0.16 - 0.20 mm

    Daniel, the shim sizes are given in millimeters, but with no decimal (e.g. 275 shim is 2.75mm thick).
     
    Last edited: Sep 3, 2018
  5. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    You guys are awesome thanks for the reply I'll check the mixture screws the pilot jets were all clear and clean so maybe the floats are indeed off and sadly I dont have an owners manual but will source one. She's had a rough life and I'm sure the valves will be out of spec.
     
  6. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Pardon the next newb question but the carbs are disassembled are the flot jets pictured below supposed to have o rings. None of mine did so in assuming that could be why the bike ran rich?
     

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  7. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    The carbs on your bike use either a fiber washer, or an aluminum crush washer to seal the float needle seats. No o-ring is used.
     
  8. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Thanks k-moe looks like a bit of finagling in my future to get her on her wheels again last question I promise lol would the valves being far enough out of spec cause a rough/no start condition?
     
  9. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    They could be. Hardly anyone checks and adjusts the valve clearnaces when they are supposed to.
    It's much more likely that the pilot circuits are dirty.
    Were the carbs fully broken down into individual parts for cleaning?
     
  10. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Not completely I took the diaphragms out removed the jets and float assembly if there is more I need to do I'm all ears the pilot jets looked great but I guess the circuit could be clogged elsewhere thanks again for the help and wisdom i guess fuel injection is worth the cost
     
  11. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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  12. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Ok everyone here is the pics even the smallest feeler wouldn't work on the shim meaning they are beyond out of spec I want able to remove the shim with a cable tie so I ordered the tool.
     

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  13. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Both lobes were facing away so I did everything right I guess these are the factory shims which explain the terrible running and idle.
     

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    Last edited: Sep 24, 2018
  14. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    You have the cam lobe oriented incorrectly. You have the cam nose about 90º from the shim, it needs to be 180º from the shim.

    Like so:
    [​IMG]

    from:Bigfitz's AIRHEAD VALVE ADJUSTMENT with Pics - parts I & II
     
  15. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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  16. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    And I prefer using the ziptie
     
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  17. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    But we both like burbon.
     
  18. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Ahh ok thanks for the heads up lol j just earned myself the noob of the year award for that thanks guys and I'll give the zip tie a shot
     
  19. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    And bacon
     
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  20. Daniel Scott Merrill

    Daniel Scott Merrill New Member

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    Ok I'm back again and apologize again for likely a newb question. I've got feeler measuring for both cylinder 1 and 2 shims but cant seem to remove shims from cylinders 3 and 4 even with my ziptie dongle worked on the first two and seems to work on 2 and 3 but the shim gets caught on the cam do I need to oil the shims and lobe? The bike is not on the center stand so the oil leans on cylinders 1 and 2
     

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