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YICS- NoN yics Interchangeable?

Discussion in 'XJ Technical Chat' started by Reason, Jun 10, 2014.

  1. Reason

    Reason New Member

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    Ive been reviving an 81 xj650h (4h7-116-xxx)

    Im wondering if anyone can help me understand the differnces in the two types of motors and which of the parts might interchange from newer models back to the '81 650/ Im wondering if i can flip the 82 intake boots upside down to fit the 81 on the left side...
     
    Reason, Jun 10, 2014
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  2. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    No, you can't. They have an "angle" to them as well, they won't fit upside down.

    The primary differences are in the cylinder bank and cylinder head castings, as well as most pieces associated with the head, like the intake manifolds, valve cover and hold-down bolts, etc. Plus they went to an electronic tach on the later (YICS) motors thus eliminating the mechanical tach drive from the head. The TCI unit may also be different between the YICS 650/750 and pre-YICS 650s; not 100% sure without looking it up.

    So, motor-wise, pretty much everything from the cylinder base up isn't interchangeable.
     
    bigfitz52, Jun 10, 2014
    #2
  3. MiGhost

    MiGhost Well-Known Member

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    The TCI is different also. Common only to the non-YICS bikes.
    80-81 650 maxim, and midnight maxim
    82 650 seca non-turbo

    Ghost
     
    MiGhost, Jun 11, 2014
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  4. RobbieRobot

    RobbieRobot Member

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    When I swapped my blown yics engine for a non-yics in my cafe racer I didn't change the TCI unit. Sometimes it ran ok but it would frequently fire on only 3 then 2 cylinders. With the bike running pod filters I had suspected these to be the cause but as soon as I swapped the TCI unit to the one from the non-yics bike the misfire cleared and the bike has been close to perfect ever since with no sign of the misfire.
     
    RobbieRobot, Jun 11, 2014
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