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If it runs like its lean, but its not

Discussion in 'XJ Technical Chat' started by e13design, Mar 10, 2019.

  1. e13design

    e13design Member

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    Hi all,
    Back again with another issue (read:a real head scratcher).
    Lets start with what the issue is;
    The bike runs good, but the idle will stick at 3000 when the bike warms up. I can force it back down by ridding the clutch and it will eventually run at 900 (my normal preset).
    Now this makes me think its an air leak, but i cant find it. The bike was not starting in the fall and i was push starting it a lot.
    Here is what i have done so far:
    *Valves checked (within spec)
    *Compression checked (within spec)
    *Spark plugs changed and gapped to .028 (all 4 look the same color)
    *Timing checked (within tolerance)
    *Carbs zestfully clean pistons drop with a nice thud sound.
    *Carbs synced with manometer and port blocker.
    *Air mixture screws set to 2.5 out.
    *Sprayed WD-40 on all rubber parts with no change to high idle. (Worked when one carb boot had a crack in it 10 years ago).
    *Airbox checked, filter looks good.
    *No change in enviroment or altitude.
    *Temp probe on 4 exhaust pipes and found that 3/4 run cooler than 1/2 and 2 is hotter than 1. I dont know if this is normal spec.
    *Issue was not present when YICS port blocker tool was inserted. (checked for air leak here after sync).

    Seriously cannot figure out where this is coming from. Im worried i have a crack in the engine, but i cant see and oil leak anywhere.
    Ive had the bike for 10 years and getting to my whits end.

    If anyone is in the LA area, or knows someone i could really use help. No shop will take a bike this old, or they want $600 just to clean my carbs.
     
  2. k-moe

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

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    That the problem went away with the YICS ports blocked tells me that the crush washers for the YICS gallery bolts need to be replaced, or that there is a crack in the casting.

    Also note that WD-40 is not the same all across the country. There is a non-flammable version, and I think that's the only version sold in California now.
     
  3. Jetfixer

    Jetfixer Well-Known Member

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    The butterfly seals on the throttle shaft is most likely source of air leak , you do not state carbs have been rebuilt , to replace you have to "break the rack" and pull the butterfly plate , there is an inner and outer seal . Xj4ever has the seals , when I did my carbs the old seals were rock hard . The other thing is the carb boot gasket , and are your boots weather cracked? A smear if RTV can help if you get real creative a bicycle inner tube attached over boot makes a good repair.
     
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  4. Polock

    Polock Well-Known Member

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    re-sync without that yics tool
     
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  5. e13design

    e13design Member

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    If the WD-40 is flamable or not wouldnt it still block up minor air leaks for a moment to let me know where the leak is?
    The washers seem to be intact but i will check again.
     
  6. e13design

    e13design Member

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    Honestly have never broke the carbs apart, ill check those seals with my WD-40 trick.
     
  7. k-moe

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

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    Nope.

    The crush washers are meant to be a one-time use thing, thouhg they can be reused a few times without issue. The thing is that you don't know how many times they have been used. There have been a few cases of a PO overtightening the plug and cracking the casting. Inspect carefully.

    If all is well there then the throttle shaft seals are the next (and honestly most likely) candidate for the cause of a vacuum leak. The trouble is that the seals might be fine at idle, but leak as the throttle plates are moved. You might not find the leak by using a spray cleaner or propane, which is why I tend to reccomend replacing the throttle shaft seals as a matter of course. The seals are cheap, and having the carbs apart more than once is a real bother.
     
    Last edited: Mar 10, 2019
  8. e13design

    e13design Member

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    I thought that was counter to how the bike us meant to be tuned.
     
  9. k-moe

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

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    Hardly anybody uses the tool. There is so little difference between using it and not using it that it's probably only necessary if you were ever to need to pass an emissions test.
     
  10. Polock

    Polock Well-Known Member

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    exhaust pipe temps are ok but there's too many variables to really be useful.
    the tool changed something, but, you don't have it going down the road. you want it to be right while your riding so you tune it that way
     
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  11. McTavish

    McTavish Active Member

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    I recently had the same issue . I replaced /installed new [chacal], 4 mixture screw o-rings, 4 mixture screws, 4 mixture screw springs, 8 throttle shaft seals, and fuel rail o rings while I was at it. and poof my my problems went away.
     
  12. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    https://www.xjbikes.com/forums/threads/yikes-all-about-the-yics-system.14757

    Executive Summary/important points to consider:

    An Insight From One Who Knows:

    To review:

    According to Yamaha, the function of YICS is to promote more complete combustion at low to mid-range rpm by swirling the mixture around the combustion chamber. They never made any direct power claims -- the system was promoted as increasing mileage up to 10 percent and promoting lower emissions through a cleaner burning charge. The increase in mileage was not through leaning out the mixture -- the increase in mileage and reduction in emissions was because less throttle was required to maintain cruising speed. They could use the same cam timing, jetting, etc. (for performance) and still meet EPA regulations. Yamaha stated that the greatest effect was while cruising at 50 to 60 mph.

    The swirling accomplishes two tasks: first, it assists mechanically in atomization of the fuel and second it speeds and distributes the flame front (and therefore combustion pressure wave) more evenly throughout the cylinder. The later "Genesis" (water-cooled "X" engines) design accomplished this even more effectively through the 5-valve design, which accomplishes the same task through a wider rpm range.


    To blank or not to blank (during engine synch), that is the question: Ok, what is the function of synchronizing? Manufacturing tolerances and wear. Multiple carbs offer the advantage of increased power and performance over the single carb configuration for reasons beyond the scope of this discussion. But at a cost.....

    As each carb is dealing with a fraction of the total air and fuel flow requirement, each carb must meter things in fractions of the total. That makes for some very tiny tolerances. In effect, we have 4 separate engines -- and if one is fighting the others, then we are wasting power and fuel and are worse off than we would be with a single-carb setup! So it is crucial that each one be perfectly adjusted and that all 4 then be synchronized to work in perfect harmony.

    So, how can we reliably adjust an individual carb based on the results of the adjustments, if it's companions are contributing to the results? Now, to be fair-----if the bike has been reasonably well maintained and the cylinders are all fairly close to begin with, you can usually get away without blanking the YICS passage and still achieve a reasonable state of tune. At the opposite end of the maintenance spectrum, the YICS passages are often already plugged up with years worth of accumulated grunge and grime, so the bike is effectively being tuned with the YICS system disabled and the presence of the tool is irrelevant. But we have seen some examples of carbs where one cylinder was effectively relying on it's neighbors to supply most of the mixture through the YICS system, and this most certainly affects performance, especially the top end.

    So, my recommendation: for an engine with approximately equal compression across the cylinders and valve clearances in spec, make sure the YICS passages are clean and use the blanking tool to tune the carbs.
     
  13. e13design

    e13design Member

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    Bump, bump bump.

    Ok boys and girls. Two weekends to change the throttle seals. And Guess what..... The throttle still hangs.
    I swear the carbs could not be more clean, the rubber manifolds are near perfect. Valves are great, spark plugs new
    Im at the end of my rope here. About to part out the bike and go buy a royal Enfield.
    Someone please talk me down off the ledge.
     
  14. e13design

    e13design Member

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    Oh sorry, also replaced the feul mixture o rings while i was at it.
    So i ask again, if it runs like its lean but its snot.
     
  15. k-moe

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

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    Remove the throttle and choke cables. Work the throttle linkage by hand.
    Does the idle still hang?
     
  16. e13design

    e13design Member

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    Yes sir. I have discovered a strange one though. If i i keep the RPM below 3000 when its warm it wont hang.
    Now one would think this is a faulty (sticking) float piston. But all i can say to that is the clunk test passed on all 4 without issue.
    And yes all 4 butterflys swing back nice and quick.
     
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  17. fiveofakind

    fiveofakind Well-Known Member

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    So it hangs when you first start it......you choke it to start ....after warm up......you back off choke and it is hanging at 3k ????

    We need more info
     
  18. e13design

    e13design Member

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    Yep,
    Read the initial post.
    Bike acts fine, all typical items have been checked verified or replaced.
    It does not hang at 3000, the throttle in general hangs as if the bike is running lean, but only if and when I am riding it and i pass the 3000rpm threshold.
    Outside of that i have the idle set at 900rpm (ish).
     
  19. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Check the fuel levels in the bowls.
     
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  20. e13design

    e13design Member

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    Hmm, i did a bench level check. I could do a drain tube level check in the morning.
    Are you thinking the feul is being restricted?
     
  21. XJ550H

    XJ550H Well-Known Member Premium Member

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    if fuel is to low in bowl it you will run lean if fuel is to high you will run rich
     
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  22. Polock

    Polock Well-Known Member

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    there's thick and thin springs on the balance screws, the thicker one goes by the screw head.
    the needle jet needle can get stuck up inside the slide, push them up and make sure they spring out.
    look into this
    might be the mixture because 900 rpm on 2 cylinders firing becomes about 3000 rpm when all 4 fire
     
  23. e13design

    e13design Member

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    Can you clarify "there's thick and thin springs on the balance screws"
     
  24. Polock

    Polock Well-Known Member

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    look close at the diameter of the wire the springs are made of
     
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  25. XJ550H

    XJ550H Well-Known Member Premium Member

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    look at the carbs in this post. warning you gotta wear shades;) notice the difference in the springs


    OWWW, My Eyes!
     
  26. Polock

    Polock Well-Known Member

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    do the plugs look like it's lean?
     
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  27. e13design

    e13design Member

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    So, just for fun. I pulled my spark plugs after killing the engine at 6000rpm. Seemed a touch lean so i took my screws from 2.25 turns out to 2.5 turns out to make it more rich.
    Then I tried again when the idle was hanging.
    Bad news, it looks about the same. They are all a nice light brown. See photos.
    Clockwise from top left 1,2,3,4.
    Darker photos (at night) are engine at idle hang.
     

    Attached Files:

  28. Dtperrell

    Dtperrell Member

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    I've also been having this same issue with my 81 XJ550. Replaced all of the seals in the carburetor except the mixture screws which I could not seem to get out and the idle will jump up when I get it over 2000 and hang around 4000 until I cut it off. Spark plugs look lean when I look at them but messing with the mixture screws does nothing.

    Correct me if I'm wrong but if it starts to act lean like this and you apply the choke shouldn't that correct the situation and bring the idle back down? I've tried this and it only made it much worse...

    Next thing on my list to try is putting the smaller jets back in. After changing to pod filters and 4-1 exhaust I went to 120 main and 37 pilot.
     
  29. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    This indicates that your pilot fuel circuit is dirty/plugged internally, or missing/damaged O-rings on the mixture screws, etc. You'll have to get those puppies out of there to inspect/replace/clean.....


    No, applying choke creates an additional source of fuel, which typically will raise the RPM's (especially in a situation where the pilot circuits aren't fully working, and hence the engine is running very lean (which also causes a run-away idle). On the bright side, it means that the starter jet passages are not plugged up, which happens.


    No, the next thing on your list should be to solve the underlying problems! Otherwise you'll end up creating more issues and chase your tail forever. A proper cleaning/rebuild, followed by an engine synch is what the doctor prescribes.
     
    Last edited: May 8, 2019
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  30. k-moe

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

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    Please keep this in your thread. It's too easy to mix up which bike we're talking about when you add a question to someone else's thread. It also divorces your question from all of the context (and related work) that we've been using to help you solve your problem.
     

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