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Vacuum Syncing

Discussion in 'XJ Technical Chat' started by MisterShah, Apr 23, 2012.

  1. MisterShah

    MisterShah Member

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    Hello everyone,

    Well after much work I have my bike running, and running well enough to idle:

    Re-shimmed valves to spec,
    Cleaned/Rebuilt Carbs,
    Clunk test passed,
    Wet set floats to spec,
    Bench synced,
    Completely stripped out old Kreem liner from tank,
    Removed rust with phosphoric acid and conditioned tank with premix.

    She started right up and idles at 1000 rpms, but she stutters. I had to take her for a spin around the block to get that out of my system. When I would stop the bike on my little spin, the engine would start revving pretty high. On inspection I noticed that the vacuum line from intake boot to petcock was not connected accidentally. Hooked it up, and issue resolved.

    Last night I made myself a Manometer so I can sync up the carbs:

    [​IMG]

    Now that I have that made, I have some questions.

    I know that I need to remove the vacuum caps off the intake boots and connect the ends of the manometer to them. Do I remove all caps when I do this, or just the two I am syncing (as I only made a two carb tool)?

    Also, what order to I sync?

    Any input or feedback would be appreciated. Thanks!
     
  2. tskaz

    tskaz Active Member

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    Only the caps you hook the manometer to.

    sync 3-4, then 1-2, then 2-3
     
  3. mlew

    mlew Well-Known Member

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    Syncing is much easier with the take off so rig some sort of fuel can to the carbs. You will need some sort of restrictor in the tubes , The spray straw from a carb cleaner can works good, hold it in the tube with some epoxy glue.
    Sync two carbs at a time with the gauge hookes to those two. Generally in this order.
    Sync carbs 1 and 2 with the screw between them, then 3 to 4 with the screw between them, then bank 1&2 to 3&4 with the screw in the middle. Blip the throttle ocationally and see if the sync holds while doing each one.
    re-adjust idle speed and mixture may be necessary, if you do then check sync again.
     
  4. MisterShah

    MisterShah Member

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    Went through vacuum syncing and having some issues.

    Bike warmed after a 5 mile ride. Box fan on engine, charger to battery, petcock to PRI, idle at about 1100.

    Synced 3/4, then synced 1/2. Then tried syncing 2/3, but when I get vacuum level between the two banks the bike wants to die at 1100 idle. She will stay on if I adjust the idle to about 2k, but I know that's not where the idle needs to be.
     
  5. MisterShah

    MisterShah Member

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    Haha! I figured it out. Blipping the throttle and adjusting idle in between makes all the difference. That and teeny tiny adjustments! All set! Now for some plug chops.
     
  6. MisterShah

    MisterShah Member

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    Alright, maybe I don't have a handle on this yet. After taking out the bike for a test run I can definitely feel an improvement in the overall smoothness of the engine. However when I stop, the idle is back to low and without feathering the throttle she feels like she's gonna die.

    I haven't started messing with the air mixture screws yet, they are still at 2.5 turns. Is this a good place to start? Do I adjust these while vacuum syncing?
     
  7. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Did you try simply turning the main idle knob in JUST a hair?

    It's much easier to leave the vacuum sync and mixture adjustments as separate processes.

    You can tweak mixtures based on reading your plugs, doing plug "chops," by ear the old-school way (known as the idle-drop method) or by the use of a Colortune. (Or use an EGA like Yamaha did.)

    Once the mixtures have been tweaked, it does pay to go back and touch up the sync.
     
  8. MisterShah

    MisterShah Member

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    First, I apologize for the novel that is about to follow. Having said that: away we go.

    I never got my idle where I wanted it to be (1050 +-50).
    Whenever I would get the idle to 1050-1100 the engine would just die on me.

    I decided to pull the carbs, check everything out, re-bench sync, and put em back on to re-vacuum sync. Floats still good & set. Jets still clean. Carbs still clunk.

    As soon as I started up the bike, she idled like poo at about 1.5K. I expected that. But then after about a minute the engine would rev to about 3K and wouldn't drop. I killed the engine, lowered the idle knob, and tried again. Back to 1.5 or thereabouts. Fine. Just for S&Gs I tested for vacuum leaks with starter fluid at each manifold boot, and between each carb body. Nothing.

    Continued letting the engine warm to running temp, and it's on to sync town to get funky. I'm jazzed.

    Started with my new vacuum gauges I picked up today. Needle fluctuated like crazy, so I made Rick's restrictor tubes and put em in, but it still fluctuated too much. Put small bits of cloth before the restrictors, and that calmed the fluctuations down...too much I think. Each carb was pulling the same according to these gauges but the engine was still rough. Finally I said to heck with this and went back to the bottles.

    Started with 3&4. Got them level. Went to 1&2. Got them level. By this time the idle dropped and the bike was dying so I adjusted the idle knob a bit at a time til it was at about 1100. Went to 2&3. Got them level. Bike still rough. Went back to 3&4. They were a little off, made adjustments and went back to 1&2. They were still good. 2&3 off a tad, adjusted and idle dropped again. Adjusted idle knob again, synced 2&3 and engine still was rough. I played this game at least one more round.

    Jeez. :roll:

    Checked 3&4 again, and they were off again. I adjusted them, and then the bike revved to about 3K again and wouldn't drop. AAAAAAH!

    WHISKEY. TANGO. FOXTROT. OVER. I threw in the towel for the night.

    Any ideas guys? If my head weren't so naturally aerodynamic, I would be ripping my hair out. I feel like I'm close every time...but I'm missing something...
     
  9. wizard

    wizard Active Member

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    I don't know where, but you are getting some air in there, that lifts the revs which activates the slides & away you go. Check shaft seals for leaks.
     
  10. MisterShah

    MisterShah Member

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    Wouldn't spraying starter fluid in between carb bodies cause a rev if the shaft seals were leaking?
     
  11. IvarNelson

    IvarNelson Member

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    I had a similar problem before i got my float levels corrected.
    But since you stated that float levels were checked...
    Just my 5 cents
     
  12. iwingameover

    iwingameover Active Member

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    Time to adjust your pilot mix screws. Get it to idle and bring them out slowly no more than 1/4 turn at a time. You should hear the difference.

    Rick's tune by ear, to save searching.

     
    Been.jamming likes this.
  13. KrS14

    KrS14 Active Member

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    I've had the best luck with setting idle mix this way ^^^^^^ Give it a shot.
     
  14. MisterShah

    MisterShah Member

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    Thanks for the replies everyone.

    Well, after taking some ZEN time this morning over coffee I remembered that my "valve chatter" was a little louder than I remember it, particularly on the right side of the head. I thought it might just have been that the sync was so far out...but this morning I decided to check my clearances again.

    All were good except for E4. It was at about .15 clearance (too tight). I am going to go pick up a 255 shim to replace the 260 that's in there now on my break. Funny that adjusting this carb is when all hell breaks loose.

    Would this be enough to knock my sync off and give me such a PITA?

    Also, building a 4 bottle system today. Sick of stop and go adjusting.
     
  15. wizard

    wizard Active Member

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    Yeh, always, valves in spec first.
     
  16. MisterShah

    MisterShah Member

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    Right, I did get my valves in spec first...or so I thought. Looks like I put the wrong shim in that E4. Next time: check, and RE-check.

    I have the correct shim now and I am doing it first thing...

    Ultimately, my question is would one valve clearance being out of spec be what is fudging up my sync?
     
  17. wizard

    wizard Active Member

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    No, you're getting unwanted air, or it can be one butterfly just holding open, that would start the same cycle of events.
     
  18. MisterShah

    MisterShah Member

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    If it's air it only comes in when I adjust the 3&4 bank...not when I adjust any other bank or pull the throttle and release...and with starter fluid test I can't detect it...

    If it is the throttle shaft seals, is there a better way (other than breaking the rack) to test for leaks?
     
  19. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Here's the thing with worn out/cracked/dried out throttle shaft seals: They're almost impossible to "detect" at rest.

    What happens is the seal will take a "set" at the position it spent the most time in relative to the shaft. Sometimes they dry out, crack, and become a collection of little dried out rubber rings.

    Anyway, they will work reasonably well until you ROTATE the throttle shaft. Sometimes even a degree or two will do it. And in the rotated position, they fail to work (as in SEAL) but at rest--- they'll fool you every time. This may show up coming off idle, or only when you whack it WFO.

    Here's the only test for throttle shaft seals, and it's a half-way deal at best:

    Take the E-ring ("C" clip) and thin fiber washer off the shaft on the outsides of carbs #1 and #4. Have a look at the seals. If you're a hopeless optimist, carefully pop them out (use a moistened toothpick, they're soft.) If those seals are good, you have a 50-50 shot that the other 6 might just be OK too. If those two outer seals are bad, then guess what: the other 6, which have a had a harder life, are bad too.

    Here's the kicker: Just because the outer two are OK, does NOT mean the others are too. The further in the rack you go, the harder the life they've led.

    Then again, they could all be fine (for now anyway, they are 30 years old.)
     
  20. MisterShah

    MisterShah Member

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    Got my valves all cleared up now. Even though it was only 1 that was out of spec, I knew it was critical.

    Getting ready to take off the carbs to re-inspect them, I noticed this little gem:

    [​IMG]

    This damn thing was such a PITA to get on there the both times I re-installed these carbs. The first time I boiled the boot and it stretched on there and stayed. This time, I didn't.

    I know it might be a stretch, but could this be my vacuum culprit? Unrestricted, unfiltered air going into Carb#2? Just trying to eliminate all possibilities before breaking the rack, as to me that is the last resort.
     
  21. biggs500

    biggs500 Active Member

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    Absolutely get that boot to fit. It's not helping as it is in the picture.
     
  22. MisterShah

    MisterShah Member

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    See, I figured that was a problem...but would a leak on the airbox side of the carbs be what is causing a rev?
     
  23. wizard

    wizard Active Member

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    No, that won't cause the high revs.
     
  24. MisterShah

    MisterShah Member

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    Didn't think so.
     
  25. Durk

    Durk Member

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    How are the intake manifold gaskets? If one (or more) is bad it will send you revving away when you sync.
     
  26. MisterShah

    MisterShah Member

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    They seem good. No cracking or warping that I can see, and no revving when I spray them down with igniter fluid...
     
  27. biggs500

    biggs500 Active Member

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    At this point Shah I would order some throttle shaft seal and replace them, then you've ruled that out. It's not hard, just a bit time consuming and it will give you a chance to clean some of the hard to reach places on the carb bodies. Be sure to replace the fuel pipe o-rings and the butterfly screws also. Get the Allen head ones and a 2mm T-handle Allen wrench and don't forget a drop of blue thread locker. Take lots of before pictures, this will help tremendously with re-assembly.

    Be sure to put the butterflies back in correctly as they are beveled and make sure they close completely after they are tightened down. If they don't they're not seated quite right. Very important. I found a good way is to take each individual carb body and look though it, actually press it up to you eye and you should see no light leaking through. If you do you'll get air as well.

    Also use a bit of silicone grease (it's in the plumbing section) on the shaft seals and where the seal sits in the carb body. Just on the seals, not the shaft and the bore hole. You want this to rotate very freely.

    This will help:

    http://www.xj4ever.com/hitachi%20thrott ... 0seals.pdf

    [​IMG]

    Good luck! :)
     
  28. MisterShah

    MisterShah Member

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    That doesn't seem too bad! Looks like I've got some parts to order. (again)!

    Soon I'll be riding my bike more than working on it! *crosses fingers*
     
  29. MisterShah

    MisterShah Member

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    Alright, went out and did an inspection. C1's spark plug shows a lean condition for sure. Also Carb#1's outside throttle shaft seal is visibly wet with gas. I think it's fair to assume that these seals are done.
     
  30. MisterShah

    MisterShah Member

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    Seals getting delivered tomorrow. Got the carbs off the bike and started disassembly. I'm having a hell of a time getting the mounting screws out. These bad boys are seized. Any tips getting them out? I don't want to munge the heads...
     
  31. wizard

    wizard Active Member

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    Impact screwdriver.
     
  32. biggs500

    biggs500 Active Member

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    Yes, try the impact driver but if that doesn't work very carefully heat them with a propane torch. Be sure to remove the diaphragms first.
     
  33. biggs500

    biggs500 Active Member

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    And remember that these bodies are aluminum, it doesn't get red before it melts so there is no outward sign that you're too hot. All you want to do is soften the locktight. A one to two second heating should suffice.
     
  34. MisterShah

    MisterShah Member

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    Thanks guys. Impact screwdriver worked like a charm.

    Question: Do the throttle seals go in with the indent "v" facing the carb body or facing out?
     
  35. biggs500

    biggs500 Active Member

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    Out. You want incoming air pressure to form a tighter seal. The ones Len sells aren't an exact duplicate. They look more substantial and when I examined them under a magnifying glass they have a channel in both sides so to me it looked like they can go in either way. Mine don't leak so I'll stand behind that claim.

    Also I replaced all the screws with Allen head bolts. Looks nicer and will make any future maintenance easier.
     
  36. MisterShah

    MisterShah Member

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    Ok. Got throttle shaft seals replaced. Started the bike up, and the idle still surges mildly for about 30 seconds with gradual creeping from about 1500, then up to 2K. After about 30 seconds of hunting she revs to about 3-3500RPMs. Looks like the seals weren't the culprit.

    So again:
    Valve clearances are within spec.
    Floats wet set.
    Diaphragms look fine. No pin holes up to light, no tears.
    Pistons clunk.
    No revs when igniter fluid sprayed around manifolds.
    All vacuum caps new and on.
    Throttle shaft seals replaced.
    Mixture screws 2.5 turns out. O rings good.
    Butterflies fully snap down when throttle released.

    Where do I go from here?

    Things I know need to be done:
    Need new air filter. (shouldn't cause revving)
    Missing a couple of exhaust header bolts (could this be an air leak that would cause this??)
    Carbs now need vacuum sync (don't want to do til engine stops revving)
    Mixture adjustment (can't do til carbs synced)

    I need ideas guys, I'm getting awfully frustrated. Where else could a vacuum leak exist that would cause this revving?
     
  37. wizard

    wizard Active Member

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    These are the facts: If the butterflys shut tight the motor cant rev, maybe one of those suckers is holding the others open slightly (doesn't take more than a crack) when the revs pick up the vacuum lifts the slides & away you go
    Have you got enough thread on the idle screw to back the butterflys to closed ?
     
  38. MisterShah

    MisterShah Member

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    I do, I will give it a shot tomorrow. With the butterflies fully closed, that would mean it shouldn't idle at all right? Before putting the rack back on the bike, I made sure the butterflies fully closed when the idle screw was backed off. Also, the butterflies snap back all the way down when released, I verified this several times before putting the carbs back on.
     
  39. MiGhost

    MiGhost Well-Known Member

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    Just an observation here.
    I did not notice bench sync in the list.
    This gets all the butterfiles at the same approximate closing, and eliminates the one butterfly holding the others open problem.

    Ghost
     
  40. MisterShah

    MisterShah Member

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    Good catch! Yeah, I bench synced them before putting them back on.
    Used the business card method.

    I'm gonna take 'em off again in the morning and go through them. There must be something I missed. While I have them off I'm gonna re-check the floats and RTV the intake manifold boots just to be sure. Eliminate everything I can and cross it off the list...

    Again, if I had hair I'd be ripping it out. I picked a bad day to quit huffing glue.
     
  41. MiGhost

    MiGhost Well-Known Member

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    With the shaft seals replaced, and the carbs bench synced. The only other place for a vacuum leak would be at the carb boots, or boot gaskets against the head.

    It would have to be a post carb air leak to cause that much rpm change. Try starter fluid where the carb boots meet the head.

    Ghost
     
  42. Durk

    Durk Member

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    When I suggested the manifold gaskets on page 2 you described the boots that are over them. The gaskets wouldn't crack, they'd most likely disintegrate after 30 years. I'd replace them that's your biggest culprit for a vacuum leak now. Yamaha has updated them the ones I bought are a more rubbery material and a little thinner.
     
  43. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Since you're going to have the rack off anyway, ensure the butterflies are truly closing.

    Back the throttle stop knob off all the way, so that they should be fully closed. Shine a flashlight in from the other side and see if any of the butterflies are maybe misaligned so that closed isn't closed.

    Don't use the "feeler" method to bench sync-- use Polock's method of comparing the butterflies' positions to the tiny bypass holes in the top of the carb throat. Be sure when doing the bench sync that you have the throttle stop turned IN enough that when turned out, the linkage can close fully. It's easy to "run yourself out of adjustment" when doing the bench sync.
     
  44. MisterShah

    MisterShah Member

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    I was under the impression that by doing this I'd be running the very likely risk of breaking the mounting bolt...
     
  45. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    That too.
     
  46. MisterShah

    MisterShah Member

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    You agree with me Fitz? I was going to RTV the boots, particularly where they meet the head...
     
  47. MisterShah

    MisterShah Member

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    Alright all, last night I RTVed where the intake manifold boots meet the head. Out of curiosity though, I took internal pictures of the manifolds, and now I am a bit worried. Take a look:

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    #3 in particular is concerning. Looks like the interior is warping pretty bad. From the outside there are no signs of this warping though.

    Is RTV going to be enough?
     
  48. biggs500

    biggs500 Active Member

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    You will certainly have some disrupted airflow. Replace the intake boots. I know they're a bit expensive but you'll be glad you did. If I recall from earlier post you're concerned about not being able to get the bolts loose. Have you tried? When I replaced my boots in 2009 they loosened up without a fuss. And my bike sat outside year round for a seven year period in the late eighties to mid nineties (again, not recommended ) when I didn't have a garage.
     
  49. MisterShah

    MisterShah Member

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    I haven't tried...basically reading about the horrors of twisting bolts. Don't want to make things worse. I may give it a try tonight though. At the very least I'd feel better taking them off and giving them a good seal of RTV between the boot and the head. From the pics you can see the o-rings are toast. At this point with the vacuum leaking I can't ride it anyway...
     
  50. MisterShah

    MisterShah Member

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    These bolts look exactly the same as the bolts that hold the valve cover on. Those bolts were a PITA, but came off with no real problems. Just out of curiosity, are these bolts different in any way? Or are the head bolts also prone to twisting?
     

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