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82 XJ550 Maxim Running Lean

Discussion in 'XJ Technical Chat' started by Catphamileez, Sep 14, 2020 at 4:04 PM.

  1. Catphamileez

    Catphamileez New Member

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    I have a 1982 XJ550 that I've been working on for a little while. When I first got it, it would rev too low and die if i didn't constantly give it some throttle. I opened up the carbs and cleaned them. When I reinstalled, the bike ran well. However, the idle was pretty high at 1500rpm. Now, if I turn it on, it will start out at about 1000 and slowly make its way up until it's at about 5000rpm and won't lower until it cools. I have tried adjusting the idle speed screw to no avail. I'm right in the middle of adjusting the valves, but I wouldn't think that would cause this.
    The caps on the little metal nipples for synching the carbs are pretty hard, and I've read that can cause vacuum leaks. I also left the carbs together and dipped them when cleaning, which I have read can damage some seals between the carbs.

    Anyone have advice on how to fix this idle?
     
  2. k-moe

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

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    You have a vacuum leak (or more than one).

    Start with the easy things. Replace the vacuum caps and the vacum line to the petcock.

    Since you dipped the carbs with the seals in place you should not be surprised if that does not remedy the problem.

    Once the carbs are eliminated as the problem you should examine the intake boots for deep cracks. Carb cleaner methodically sprayed around each boot in turn will identify any that are cracked clear through. There is a budget-friendly repair if you can't afford to buy new replacements, or if you're hesitant to remove the bolts that hold the boots on (they can break pretty easily).

    Carbs should be first though.

    Read This First

    Inside your Carbs

    IN THE CHURCH OF CLEAN

    Cleaning your Mikuni carbs

    Why you should replace butterfly (throttle shaft) seals.

    Replacing your Hitachi throttle shaft seals (The same info is applicable to the Mikunis as well).

    Setting the fuel levels (this is a critical step that is often overlooked during carb work).
     
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  3. Catphamileez

    Catphamileez New Member

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    I replaced all intake manifold boots when I got the bike because they were cracked and ripped all over. I'll order shims, the vacuum caps, the vacuum line, and throttle seals from xj4ever and re-clean the carbs while replacing the seals.

    Thanks a ton for the help.
     
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  4. Minimutly

    Minimutly Active Member

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    Normally you would do a bench synch to align all the butterflies, using the transition hole nearest closed to do this, then set the idle screw to allow the least crack of light through them.
    Did you do this?
    Did you set the float levels and then check them on the bike?
    This should get it close enough to do a running sync using vacuum gauges (both my seca and maxim 650s run well enough to use by using this method).
    Lastly, did you do the valve clearances?
     
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  5. bigfitz52

    bigfitz52 Well-Known Member

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    How about slow down and take things in order?

    Replacing throttle shaft seals in Mikunis is a bit of a major project, and while I'm not going to argue that it's not necessary, or will be at some point, you're still coming at this backwards. Let's don't rush into breaking the rack just yet.
    First thing, before any carb tuning can begin, is to get the valves in spec.
    Then, once cleaned, the carbs need to have the float levels accurately wet-set and a careful bench sync done before they are returned to the bike. At that point, a running vacuum sync is in order; which could be affected by a vacuum leak if said leak is bad enough. So far, a vacuum leak, while quite plausible or even probable, has not been diagnosed, just immediately assumed based on symptoms. Symptoms that are not unexpected with unsynchronized carbs and/or wonky float levels as well.

    You can't just clean the carbs, throw them back on the bike, and hope it will run. Mikunis are very sensitive to being disassembled and reassembled; wet-set float levels and a bench sync are absolutely a must anytime you have them apart.

    One more quick note: On the 550s, the intake manifold bolt holes are "blind" that is, they don't go all the way through like on the bigger bikes. As such, they are less prone to becoming corroded in place, and easier to remove (carefully) without breaking. Replacing the manifolds on a 550 is nowhere near as scary as on one of the bigger XJs.
     
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  6. Catphamileez

    Catphamileez New Member

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    Well, I have throttle shaft seals on the way, as well as new pilot jets and pilot mixture screws as when I took the carbs apart the heads of those were in pretty terrible shape. If I take the carbs apart to replace these, should I still leave the rack intact and leave the old throttle shaft seals alone? I doubt they've been touched in a long time. A lot of small rubber pieces like that on this bike so far have been practically rock hard. Especially the ones that are hard to get to, or out of the way. Thank you for helping me see this from a different angle and please give me more advice on this part of the carbs.

    I've been busy working on the camshafts of the bike today to easily get the valve shims out (I took one out and rotated the engine so I couldn't get it back in), and now I have the shims I need coming.

    Do you have links to guides on how to check float levels and bench synch? I have seen guides for these tasks before, but sometimes I lose things like those and can't get back to them through much searching. I'll definitely do this stuff before I put the carbs fully back together.
     
  7. Catphamileez

    Catphamileez New Member

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    Okay, small problem. In my manual (Clymer XJ550), for removing the camshafts it says to remove the tensioner, bring the cams to the T on the crankshaft, remove one bolt from each sprocket. Then rotate the engine counterclockwise until the bolts on the other side of the sprockets are visible and remove those.

    However, later on for reassembling the clams, it says to make sure the cams are still in TDC position. My engine is no longer in that position because I rotated it as instructed. What do I do to proceed with installation?
     
  8. Catphamileez

    Catphamileez New Member

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    Upon further reading, it looks like it wants me to take the cylinder head off the engine and then rotate it back to TDC after the head is off. I don't have a reason to take the head off. With the chain, sprockets, and camshafts removed can I turn my engine back to TDC without removing the head first?

    Thanks for all the help everyone
     
  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    yes. remove left side crank cover where the pickup coils are located. you will see a square "nut" turn that the whay the wheels turn . on the pick up plate you will se a T that is TDC turn motor untill pointer is pointing at the T.
    remove spark plugs first to make turning easy

    the cams have a mark on them and cam caps have a mark that you line up for the cam install

    when you reinstall the cam chain tensioner you will see a C on the same plate that is where the pointer points when you release the cam adjusted
     
  10. Catphamileez

    Catphamileez New Member

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    I see that. Is it okay to turn with the camshafts out and the cam chain hanging above?
     
  11. XJ550H

    XJ550H Well-Known Member Premium Member

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    yes as all the valves will be closed. just remove sparkplugs to avoid compression.

    cam chain may rotate if it is still on sprocket on crankshaft.
     
  12. Catphamileez

    Catphamileez New Member

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    Okay, the cam chain I think is on the crankshaft underneath still. Do I just help it through my zip tie holding it by the frame and rotate to T? Sorry for sounding apprehensive and careful, I just don't want to damage my engine and I know you guys are experts.
     
  13. Catphamileez

    Catphamileez New Member

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    When I reinstall the camshafts, do I have to time them? I see they have some sort of spiral gearing, will this time them properly for me?
     
  14. Catphamileez

    Catphamileez New Member

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    I have an update. I went ahead and pushed the cam chain along slowly and turned the engine all the way around to align the T with the mark perfectly.

    Does this mean that my cylinders are in a good position now and I can put my cams back on safely? I understand how to follow the manual procedure to do this.

    Also, I still need to know how to set my float levels and bench synch my carbs. Could somebody send me links to guides on these subjects?

    Thanks everyone!
     
  15. k-moe

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

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    That I did not know. Those details are a large part of why I appreciate you being able to return to the forum.
     
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  16. k-moe

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

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    how-to-bench-synch-your-carbs.6366
     
  17. Catphamileez

    Catphamileez New Member

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    Awesome link. Now if anyone had one about how to set float levels that would be awesome, I'm pretty sure I need to buy some cheap hardware for that and I'm about to go out to the store tomorrow.
     
  18. bigfitz52

    bigfitz52 Well-Known Member

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    So h0w did we get to camshaft removal again? Just to replace shims? Valve shims can easily be changed without removing the cams.

    Yes, the "T" mark is TDC on the crank and is used for properly timing the cams. Cam timing is very important, as the pistons could hit the valves if not set up properly. Not sure why you're now contemplating removing the head, my advice there is DON'T. I'm still unclear as to why the motor is coming apart this far, seems a bit unnecessary.

    Float levels: http://www.xj4ever.com/setting fuel levels.pdf You have Mikuni BS28s, so the spec is 2mm +/-1mm bellow carb/bowl joint.
     
  19. Catphamileez

    Catphamileez New Member

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    I had to remove the cams because I removed a shim and then turned the engine without replacing it, so using the wire method I couldn't seem to get a new shim in its place. Therefore I removed the cams to make this shim job easier. I'm now waiting, with the head remaining on, for new shims so I can put this engine back together.
     
  20. bigfitz52

    bigfitz52 Well-Known Member

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    Gotcha. Another reason the "holding tool" method is a better than the "wire down the plug 'ole" method.

    Advice: if you plan to keep this bike, spend the <however much it is these days> and get a valve bucket hold-down tool. Makes the job much easier.

    Also, and again if you plan to keep this bike, invest in a factory shop manual. The Clymer, while "OK" is chock full of misinformation. (Which is not to absolve the factory book of questionable procedures either...)
     

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