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xj900 running rich what would be the cause?

Discussion in 'XJ Technical Chat' started by zblip2, Oct 7, 2011.

  1. zblip2

    zblip2 New Member

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    I'm thinking of buying a used 1983 xj900 with 45,000 mile on the counter. The owner says I'll probably have to clean the carbs cause the motor is running "rich". In my head, rich means "too much gas", and dirty carb means gas not getting through, therefore "not enough gas". Am I wrong about this. What would be causes for a motor running rich?

    Thanks
     
  2. wizard

    wizard Active Member

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    Lots of things, but check the pilot mixture screws first. Do this by turning the screws in (clockwise) until they lightly bottom & count the turns.
    It could also be floats not shutting down the fuel flow, or sticking slides, but whatever, you will still have to pull the carbs for cleaning & sync'.
     
  3. RudieDelRude

    RudieDelRude Member

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    Stock exhaust and intake?

    If the owner says "you'll probably just have to do this to fix it doing that" it means the bike probably wasn't maintained as well as it should have been. Meaning you're going to see a lot more "thats" that need fixed by doing a lot more than " just this'"

    Not tying to discourage you, but these older bikes usually need a good inspection and a little bit of work to ensure safety and durability.
     
  4. zblip2

    zblip2 New Member

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    How many turns shold the pilot screw be from bottum?

    Thanks!


     
  5. usedboats

    usedboats New Member

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    2 1/2 TURNS OUT FROM SLIGHTLY BOTTOMING OUT IS THE GENERAL RULE ON YOUR MIXTURE SCREWS IF THEY HAVEN'T BEEN TAPPED SO THEY CAN'T MOVE. IF SO, YOU HAVE TO SEND THEM OFF TO A PRO. HEAVEY GAS ON OLDER BIKES USUALLY MEANS FLOATS AND FLOAT NEEDLE VALVES AREN'T DOING WHAT THEY SHOULD. TEAR DOWN YOUR BOWLS ONLY!!! PULL THE FLOATS AND TAKE THE NEEDLE VALVES AND PUT THEM IN SOME CARB CLEANER FOR ABOUT 5 TO 10 MIN. THE CARB CLEANER HAS TO BE THE CHEAP STUFF LIKE ADVANCE AUTO'S CHEAPEST STUFF. WHEN YOU DO THAT, THE RUBBER ON THE NEEDLE TIPS WILL RECONSTITUTE. BE CAREFUL NOT TO LEAVE THEM IN THE CLEANER TO LONG AS THEY WILL SWELL UP TO LARGE TO BE USEFUL. IT'S A TRICK THAT THE CARB REBUILDERS DO AND CHARGE YOU FOR NEW ONES. YOU HAVE TO KNOW WHAT THEY SHOULD LOOK LIKE TO BEGIN WITH, TO HAVE THIS WORK FOR YOU. GOOD LUCK. MOSTLY OLD CARBS RUN LEAN FROM BEING DIRTY EVERYWHERE AND CLOGGING UP. IT'S ALL IN THE BACKFIRING...RICH IS BLACK SMOKE AND BACKFIRING AND LEAN IS NO BLK SMOKE BUT STILL BACK FIRING AND THEN YOU HAVE TO KNOW THE DIFFERENCE BETWEEN THE POLLUTION SYSTEM BACK FIRE AND THE REST. YOU'LL GET IT.BACK FIRING WHEN YOU REV IT UP AND LET OFF. DO NOT MESS WITH ANY OF THE LINKAGE OR YOU'LL HAVE TO RESYNC THE CARBS...YOU MAY HAVE TO ANYWAY.
     
  6. Bobbybonez

    Bobbybonez Member

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    Pull out your spark plugs. Are the tips white? If they are then you are running rich. Also look around on the forums for how to check your valve clearance. That should be one of the first things you do. Like Rudie said there is probably more wrong with the bike then the carbs needing to be cleaned.
     
  7. TIMEtoRIDE

    TIMEtoRIDE Active Member

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    sooty black is rich - flat white is way too lean.
    Set your plugs on brown cardboard, 1-4, post a picture.

    We're looking for a "tan" that is close to a brown bag.
     
  8. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    As above, you're going to have to do a lot more than simply clean the carbs to get it running right. Just be aware of that going in. Be sure to run a compression test before buying if possible, so you don't buy a money pit. That's a lot of miles, and things like pistons and rings are unobtanium. Be sure the actual "mill" is solid first.
     
  9. Bobbybonez

    Bobbybonez Member

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    whoops my mistake. Im still learning but it seems Im learning from the best. Thanks for correcting me, don't want to screw him up too much
     
  10. Ltdave

    Ltdave Member

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    if it is running rich i.e. more gas than air, pull the air filter out and replace it...

    even if it is a K&N reusable, if you dont know how old it is or how its been treated/handled replace it. they can be damaged VERY EASILY if cleaned and then dried with an air compressor...

    do a plug chop. get it up to operating temperature and run it around. then using the kill switch, kill the engine. youll have to pull the clutch obviously if youre riding it (which you should be with some serious but not redline, throttle)...

    do NOT restart the bike after youve killed it. lay the plugs on the cardboar for comparison. use American cardboard, not that yellow rice colored crap that comes from asia...

    if the plugs look good and it still runs funky, then check the valves and clean the carbs. once youve done the valves, install and tune/balance the carbs and then do another plug chop...

    after that? youre on your own until someone else here chimes in because thats as far as i can help...

    post some pics. i love mine but never ride it because of the other 4 bikes in my garage...
     
  11. RickCoMatic

    RickCoMatic Well-Known Member

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    The Diaphragm Pistons may become Lazy due to the Bore becoming Oxidized.

    After a long while, the Bore Oxidizes enough that the Piston does not rise and fall without being encumbered by the light film of Oxidation which spoils the free movement of the Piston. By imperceptibly shrinking the already close tolerances the Piston and Bore employ, ... the Bore "Shrinks". The Piston begins to behave abnormally.

    The Piston may begin to SHUTTER up and down.
    It may start and stop, ... or all-together freeze.

    Perform a CLUNK TEST.

    To get the MAXIMUM Performance you can achieve with those Mikuni's on a 900 ... Polish the Bores.

    Use a Dremel Tool with a Buffing Wheel.
    Treat each Bore with a Polishing after scrubbing with ScotchBrite Pad.
    Use Jewelers Rouge's.
    Number-5 and Number-6.

    ~~~~~~Scrub~~~Polish~~~Finish~~~~~~[​IMG]
     
  12. zblip2

    zblip2 New Member

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    Wow you know your bikes dude
     
  13. RickCoMatic

    RickCoMatic Well-Known Member

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    Another clandestine cause of running RICH is Clogged Emulsion Tube Air Holes.

    With their surrounding Air Holes clogged, ... FUEL, ... from the Main Jet gets drawn into the Intake Stream in a rivulet and droplets form which does not "BURN" with a powerful and efficient Mixture. The Non-atomized charge wasted gas and coats the Spark Plugs with soot.

    [​IMG]
     

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