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XJ600 Cafe Racer project

Discussion in 'XJ Modifications' started by GoCrazy, Sep 13, 2016.

  1. GoCrazy

    GoCrazy Member

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    Hey, just a quick update. I finally managed to put the engine back together and fit it into the frame .....and that is the end of good news as the engine won't start, it cranks nicely though. After some sniffing with a multimeter I found a potential culprit - ignition coils. According to the manual they primary and secondary coils resistance should be:

    Primary 2,7 Ohm (+/- 10%) --> my reading - 2,3 which is more than 10% difference
    Secondary 12k Ohm (+/- 20%) --> ny reading - 22 - 24 k ohm - no comment :)

    My question is -is it normal for out of spec coils to produce spark? I do get a blue spark, but coils readings suggest that they should be replaced.
     
  2. a100man

    a100man Well-Known Member

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    Not sure - are both coils reading the same?
     
  3. Rooster53

    Rooster53 Well-Known Member Premium Member

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    The Haynes manual I have spec's the later models primary at 1.8 to 2.2 ohms, are you sure you have the right spec.
    As for the secondary, is that with the spark plug caps removed?
     
  4. GoCrazy

    GoCrazy Member

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    These specs come from Yamaha Service Manual, I can post a screen shot :)

    I didn't remove spark plug caps ....should I ? The manual doesn't say anything about that.
     
  5. Rooster53

    Rooster53 Well-Known Member Premium Member

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    You can do it either way, but if you leave the caps on you need to add the resistance of the spark plug caps to determine if you are in spec.

    Check your manual and it should list a specification for the secondary coil and the spark plug caps.

    So 12kohm and you read 22-24 kohm with the caps on. So if the caps are 5 kohm X 2 that would be a good reading.

    Likely OK if you have a nice blue spark.

    And reading back over the thread, did you ever get good compression readings? A low compression engine is going to be difficult to start. You could try the old school method of adding a teaspoon of oil and see if it will fire up.

    Also on carb rebuild, are you certain the enrichment circuits were properly cleaned. It is often overlooked and will cause issues starting when cold.
     
  6. GoCrazy

    GoCrazy Member

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    Did some research on the ignition and coils specs. A funny thing :) Yamaha Service Manual for XJ 600 includes ignition specs ONLY for 51J models, while Haynes Service Manual specifies exact parameters both for 51J and 3KM models of XJ600.

    Yamaha Service Manual
    YSM.png

    Haynes Service Manual

    HSM.png

    So it seems that ignition primary resistance is more or less OK. As for my secondary resistance - looks like it has to be measures without spark caps, so my 24k Ohm minus 10k Ohm form spark caps results in 14k Ohm which is again more or less OK.

    Tomorrow, I'll check the pickup coil resistance and perform a compression check. I am pretty sure that compression should be fine as I freshly rebuild the engine with fresh rings, plus I gave the valve head to be machined by a professional. However, I decided not to assume anything but check everything just to be on the safe side.

    Is it possible that I have ignition timing issues? Caused maybe by 180 degrees off timing? What if I set the TDC at exhaust stroke not the compression stroke?
     
    Last edited: Aug 14, 2017
  7. Connor Skill

    Connor Skill New Member

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    What kind of forks are you running on that? Im doing my own XJ project and really love the way yours looks!
     
  8. GoCrazy

    GoCrazy Member

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    Stock forks, lowered around 5cm and powder coated. I also bought a pair of rubber boots for around 3$ in a local auto parts store ( They are from a moped or something)
     

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