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1985 XJ 900 poor running, valve timing and final drive leakage

Discussion in 'XJ Technical Chat' started by Lochraceness, May 14, 2019.

  1. Lochraceness

    Lochraceness New Member

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    Hello all :) I have what I believe to be a 1985 XJ900 with VIN number 58L000234.

    This motorcycle had been sitting a number of years when I got it, and I have done some light restauration on it. It now has some problems which are puzzling me:

    1. It starts, but will run only on choke, and it backfires also sometimes, mostly on low revs. Seems to go better on high revs. The petrol in the tank is old.
    I could not find any signs of air leakage when I had a swift visual check.

    It was also like this when I got it, but it got better when I drove it a bit; it ran fine 6 to 8 months ago.


    2. I have checked the valve clearances with a standard metric feeler gauge. All valves seems to be 'something within spec', apart from the two middle inlet valves. On these two, I can easily get the 0,05mm blade in, but not the 0,10mm. I reckon it is about 0,07mm clearance on both of them. Specs for the inlet are 0,11mm-0,16mm according to Haynes.
    Is it a good idea to try to run it like this during this summer, and set the valves next winter?
    Will those two out-of-spec inlet valves have anything to do with the backfiring and poor running?

    3. The final drive leaks, I suspect it is from the inside of the hub as I can see oil on the rim, but not anywhere on the outside of the casing of the final drive.

    Any comments on this is most welcomed.

    Also I wish everyone on there a pleasant summer, with a lot of driving :)



    Kind regards, Lochraceness
     
  2. FJ111200

    FJ111200 Active Member

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    Regarding the starting and running only on choke, it's a classic sign that the carbs need stripping and thoroughly cleaning.
    The old petrol has probably clogged up the jets and passageways.

    And have a pleasant summer yourself.
     
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  3. Lochraceness

    Lochraceness New Member

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    Thank you very much for your reply; what you are saying is great info!

    Is there any reason to believe that a can of 'seafoam' should do the trick so I can run it this summer? Thanks.


    Cheers, Lochraceness
     
  4. FJ111200

    FJ111200 Active Member

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    You could try it first. I'd try anything before removing the carbs. If it works then great, but if not then there's just the one thing left to do.
     
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  5. Lochraceness

    Lochraceness New Member

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    Ok, Thanks. I'll give it a go :)

    L
     
  6. Nuch

    Nuch Well-Known Member

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    Timbox and Lochraceness like this.
  7. Lochraceness

    Lochraceness New Member

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    Thank you very much. I will look into it as soon as possible.


    Cheers.
     
  8. Lochraceness

    Lochraceness New Member

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    Hello again :)

    I have now driven the thing a bit, and the engine now runs as it should... smooth and responsive. It also ran rough for the first few minutes of running when I first got it but then it ran fine. I have now also added a bit of seafoam.

    However, the 'neutral' lamp came on and is lit all the time; this happened while I was working my way through the gears during rather hard acceleration.
    Is this a know issue please? Any comments as to what is the most likely cause? Are exploded views of the neutral switch readily available?

    Regarding valve timing, I have decided to run it with the out of spec clearance this summer. (I reckon there are two inlet valves that are 0,07mm, the rest are within spec).

    Any comments as of how stupid or clever I am with this will be much appreciated. I may be inclined to change my view, based on the comments here.


    Hope everyone has a fun and enjoyable time riding :)


    Lochraceness
     
  9. k-moe

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

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    Dose the oil with Seafoam. The neutral switch is likely gummed up with sludge. Replacement switches are available, but replacement is not a straightforward task.
     
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  10. Lochraceness

    Lochraceness New Member

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    Thank you very much for your reply, I will do exactly what you say, sir :)


    Cheers
     
  11. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    This is a very bad idea, unless you enjoy performing a full cylinder head teardown/rebuild at some time in the near future....and don't get me wrong, although that procedure is difficult and can be quite expensive, it is a great learning experience that everyone should go thru at least once!

    Cleaning/rebuilding the carbies: one weekend.
    Setting the valve clearances properly: 2-3 hours.
     
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  12. Lochraceness

    Lochraceness New Member

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    Thank you for your input, I really appreciate it. I have no desire to do this procedure now; maybe it is very much better to set the valves now. I did have the foresight to buy the tool from ebay, so that should be ok. I just need to take out the two shims and work out how much thicker the new ones shall be.

    Thanks again for your input :)


    Cheers
     
  13. Franz

    Franz Well-Known Member

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    I got my engine out of the frame now and am going to replace the cam chain, alternator chain, chain guide and starter clutch components as soon as possible. Be fun I think. Last one I did was my cam chain on my old Honda CB750 K2. Great fun delving into engines Chacal.
     
  14. k-moe

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

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  15. Chitwood

    Chitwood Well-Known Member

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    You'll end up needing a thinner shim not a thicker one
     
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  16. Lochraceness

    Lochraceness New Member

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    Hello again all :)

    I must admit I have been very slow, but now I have started working on the bike again. I have measured the shims for the two valves that were out of spec, and will go to the local independant garage tomorrow. Inlet on cylinder number two was a 265, which I thought I'd replace with a 255, inlet on cylinder number three was a 280 which I thought I'd swap with a 270. Approximat gap on the old shims was something like 0,07 millimeter (0,10mm did not go in, 0,05 did). Does this sound right?

    Also, I wonder if anyone knows the correct dimensions for the oil seal on the final drive that has partnumber HCP9348 and o-ring HCP9765? I actually could order form xj4ever.com, but there are hefty importfines if I buy in America, and I thought I'd try the very well assorted local ironmonger.

    From memory I thought I found the dimensions on this forum, but I have searched a bit, and was not able to find it again. Thankful for any help.
     
  17. Polock

    Polock Well-Known Member

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    bmw K bikes use the same diameter shim
     
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  18. Lochraceness

    Lochraceness New Member

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    Thank you very much for that piece of information; it is good to know when I turn up at the garage tomorrow. Thanks again.


    Cheers, Lochraceness
     
  19. Lochraceness

    Lochraceness New Member

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    Hello again. The valves are now set and I have replaced the simmer ring/oil seal in the final drive. I am not entirely sure if it is leaking or not, but will know a few miles down the road (as soon as the snow has melted).

    For those of you that are interrested, the 'big oil seal' in the final drive on my XJ900 58L has the dimentions 70mm inside diameter, 90mm outside diameter and 10mm thickness. Thanks.


    Kind regards, Lochraceness.
     

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