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Carb Cync / Readings Issues

Discussion in 'XJ Technical Chat' started by jjcurtiscb, Apr 4, 2020.

  1. jjcurtiscb

    jjcurtiscb Member

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    UGH, typo in title I can't fix...SYNC...

    I went through and adjusted my valve gaps this winter, which then lead to some bike starting issues. So after thoroughly cleaning my carbs, I have finally got it running again. My problem is that now that I went to sync my carbs, I am getting some odd things (at least to me).

    When I connect the vacuum gauges and start the bike again, it revs at about 1000 rpm higher than before. Can I assume that this means the vacuum caps I have on the boots are probably not sealing properly, whereas the vacuum gauge is? Should it be revving it like that? I also had to mess with the mixture screws to get it running again (set to 2.5 turns out). I am guessing turning those in once I get the vacuum problem sorted out would be the thing to fix the revving?

    The next question is that the reading I get is at about 8 inches or so, which the meter says late valve timing or intake manifold leak. Being that there sometimes is a puff of smoke that comes out near carb two would suggest it's probably a leak somewhere?

    Thanks!
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    After you sync the carbs you will have to turn the idle down in the directions for syncing you sink and adjust the idle .
    I would not be surprised if after the removing the crusty old caps they are no longer sealing
    When you adjust the mixture screws you do have to resync. What you should really be doing is adjusting mixture screws, syncing adjust idle, adjust mixture screws and resync. You can do this as many times as you want like or just once or twice.

    You want to ignore what is written on those vacuum gauges is probably for an automobile. The goal of sinking is to match all the vacuum in all the cylinders it is not too get a specific reading of the cylinders to a certain level again it is to match them all together. You can test for vacuum leaks by spraying carb cleaner WD-40 etc around the manifold boots carb caps throttle body seals to see if you hear a change in the RPM.
     
    Last edited: Apr 4, 2020
  3. jjcurtiscb

    jjcurtiscb Member

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    Awesome! Thanks. Sounds like I’m getting closer haha!
     
  4. jjcurtiscb

    jjcurtiscb Member

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    So I have at least got it to run, and can keep it running. It still dies if I pin it and then roll off the throttle while riding. Then it takes a little bit to get started again (assuming it's trying to burn off the excess gas). New question. My bike currently runs straight pipes (came that way when I bought it) but I am thinking of getting some mufflers because my ears aren't a huge fan of the noise lol. I assume if I put some shorty mufflers on, it's going to throw a new problem into the adjustments I am doing now?

    Right now mike bike seems to still be running rich and the pilot screws are only at about 1.25 turns out. I think I read if you get that low you should rejet, correct? My question is, if I add shortly mufflers, will the mixture become more lean? As such, I would need to go even smaller on the jets?
     
  5. XJ550H

    XJ550H Well-Known Member Premium Member

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    lean comes from intake.

    1-1/4 turns go to 2-1/2 turns the screw is an air fuel mixture screw you are not allowing enough air from the air jet in and it is pulling in more fuel in the pilot jet circuit.
    unless it has a larger than expected pilot fuel jet.

    what jets are you using?
     
  6. jjcurtiscb

    jjcurtiscb Member

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    I didn’t think to look when I had it apart :(

    I guess I am confused then. If I turn them 2 1/2 out, the bike idles really high even with the idle screw turned all the way out. If I turn them out to 3 or 3 1/2 it idles even faster.

    EDIT: turned them out and it idles high as noted. Now if I take it out for a spin, it dies immediately after i let off the throttle. Like almost instant. Before it would try and hang on. It also seems to backfire more with the screws out more. Judging from the sound and spark plugs, I would guess it's coming from cylinder 4. I just did the valves before this, so could the timing be causing all of these issues? I don't have a timing gun to check that nor a colortune for original set up.

    EDIT2: Just checked compression and its about 65 in all 4 cylinders...which I don't understand how it fire up so quick with the compression being that low...Maybe I should just cut my losses.

    Clearly I don't know what I am doing so I think I will just take it to a shop.
     
    Last edited: Apr 10, 2020
  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    it could be it needs a running sync.
    compression may come up with time, or you have a bad comp tester. did you adjust the valve shims or check them?
     
  8. jjcurtiscb

    jjcurtiscb Member

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    Yeah. All of this started because I did the valve shims honestly. When I adjusted those, the bike fires up much faster, but queue all the idle / running problems. Could a bad valve cover gasket cause air or something to get in? I have the idle screw completely out and it still revs and doesn't die which makes me think there must be an air leak or something somewhere.

    When I did a running sync, all the carbs were fairly close to one another. Nothing that really screamed out of place. also, if I blip the throttle, it doesn't bog or anything. It's very responsive. It just doesn't settle back down.
     
  9. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    RICH, LEAN, or possibly even ritually UNCLEAN or OBSCENE: THE CARB REBUILDING FAQ:

    Let us begin by warning you, though: an engine that is out of synch may perform AS IF it has a lean, or a rich, or a hanging idle, or a no-idle, or a run-away idle, or any variety of different conditions------if your engine (carbs) have not been synched, then that at is the #1 issue that you should attend to first, before you even READ any of the guidelines below and go and try to adjust and fiddle with things and change settings THAT AREN'T THE CAUSE OF THE REAL PROBLEM!!

    And here are a couple of very good visuals of how a Hitachi or Mikuni CV ("constant velocity") carb actually works. For those of us who are not intimately familiar with these carbs, these videos provide a great basic understanding of what is actually "going on" with your carbs:









    Question #1: Why Isn't It Running Right?:

    Below is a semi-useful "general rules-of-thumb" list to help you recognize and diagnose fuel-mixture problems.

    All of these descriptions assume that the carburetors are cleaned and operating properly, are stock (no jet kit), the valves are adjusted properly, and the engine has been synched.

    If any of the above procedures, tasks, actions, or activities have NOT been checked or performed, then do them first, or otherwise all your other efforts will barely even give you "casino odds" at striking it rich and determining what the real cause(s) of your symptoms are......

    Here are the 3 rules you should always follow whenever trying to troubleshoot [i[anytime[/i]:





    Typical Symptoms and Causes of a Lean Fuel-Mixture Condition:

    - Poor acceleration; the engine feels flat.

    - The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.)

    - Idle speed falls after you blip the throttle, then creeps back up.

    - The engine runs hot, knocks, pings and overheats.

    - A lean pilot circuit condition can be responsible for a creeping or hanging high idle, where the rpms stay high then slowly drop down to the set point.

    - The engine surges or hunts when cruising at part-throttle.

    - Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle.

    - The engine runs better in warm weather, worse in cool.

    - Performance gets worse when the air filter is removed.

    - Fuel levels that are too low will cause a lean condition.

    - Pilot fuel circuit that are partially or completely clogged.

    - Fuel jets that are too small for your application.

    - Pilot mixture screws being set too far "in".

    - In cases where an overly lean fuel condition is suspected, the application of a small amount of "choke" may decrease or eliminate the symptoms.

    - Here's the main reason you don't want to run lean over an extended period of time:

    http://www.xjbikes.com/forums/threads/head-gasket-1982-maxim-650.85273/#post-504365

    A holed piston. Notice how it's right where the plug fires (the hottest point anyway, and made ultra-hotter by a lean fuel condition).



    Typical Symptoms of a Rich Fuel-Mixture Condition:

    - Engine acceleration is flat and uneven and loses that "crisp" feel.

    - The engine "eight-strokes" as it loads up and skips combustion cycles.

    - The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle.

    - An overly rich pilot mixture is usually the culprit when the idle drops low then slowly recovers.

    - The throttle needs to be open continuously to maintain acceleration.

    - Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel.

    - Poor fuel economy.

    - The engine works better when cold. Performance falls off as it warms up or the ambient temperature rises.

    - Engine performance improves when the air cleaner is removed.

    - Fuel levels that are too high will cause a rich condition.

    - A choke system that is slightly hung open or has leaky plunger valves. Leaky valves can be determined via a measurement of vacuum using your synch sticks (or vac gauge) --- while watching the gauge, apply a small amount of downward force on the top of the plunger valve. If it vac draw changes, the plunger isn't sealing very well. Over time a small ridge may build up on the tapered brass plunger valve surface (Hitachi carbs) that may be possible to polish out, or a deformity forms on the rubber seals (Mikuni carbs) that may be possible to reform back into shape.

    - Fuel jets that are too large for your application.

    - Pilot and main FUEL jets being reversed.

    - Pilot and main AIR jets being reversed.

    - Pilot mixture screws being set too far "out".

    - Main jet needle set at too "high” a position (on some Mikuni models), or that has "risen up” within its head cap (on Hitachi models).

    - A simple test for an overly-rich condition is to remove the air filter element, and see if performance improves. A very dirty air filter will cause an overly rich condition, AND, even if the filter was in good condition, the great increase in airflow accomplished by removing the air filter will tend to dilute an overly rich fuel mixture, and thus allow you to focus on determining the cause of that situation.



    Some common causes of a high idle:

    - Engine has not been synched, as each cylinder "fights" the others for dominance, it can lead to a run-away idle situation.

    - A lean air-fuel mixture condition, which can be caused by a variety of problems......vacuum leaks, plugged or too-small fuel jets, etc. Old or "stale" gas may also cause a lean fuel-air mixture to occur temporarily (until the fuel is used up!).

    - A vacuum leak somewhere in the intake system.....intake boots, internal o-ring seals, etc.

    - Mixture screws not properly set or adjusted.

    - Vacuum piston sticking or stuck in a partially raised position.

    - Idle speed screw set too high, or set to create a "proper" idle speed when the engine was cold (and thus results in a "high idle" once the engine reaches operating temps). The idle speed when the engine is cold should be modulated via the use of the choke (enrichment) control system.

    - Butterfly valves opened too far; synch screws out of adjustment.

    - Throttle cable wear, adjustment, or throttle lever brackets installed incorrectly or interfering with other nearby objects (cylinder head fins, etc.).

    - Choke (enrichment) circuit is stuck "open"....this can occur even if the choke lever is rotated to the fully closed position, if for some reasons the choke plungers are not fully closing (cable wear, cable adjustment, bent finger brackets, or installation problems). In addition, even if the choke plungers are "closing" fully, if the choke plunger valve face or its seat are worn or scarred, this will allow fuel to leak part the plunger and richen the mixture even if the plungers are closed.



    Why your engine seems to be schizoid:

    A hanging idle---one that stays high and slowly comes down when decelerating---is a sign of lean mixture. The opposite case, where the idle drops dangerously low then rises, is a sign of rich mixture.

    A bike that runs better when hot is probably lean, and a bike that runs better when cold is probably rich.

    But sometimes a bike that can be adjusted "just right" when cool, but actually starts exhibiting signs of running lean (hanging idle) as it warms up. And if the idle speed is then re-adjusted while the engine is warm, but eventually falls and the bike dies (especially when sitting at a stop light). Or if the pilot screws are adjusted, then it's too rich when cold---all in direct contradiction of the above observations.

    Experience shows that this is a sign of worn throttle shaft seals.....the aluminum carb bodies expand with the heat, but the steel throttle shafts---resting comfortably in a nice cool airflow---don't heat up and therefore don't expand. Once the shaft seals get old and hard, they no longer are able to flex and fill the gap.....so the carb starts drawing air around the shafts, leaning it out.



    Why does my engine sometimes backfire when I first turn on the key (without attempting to start the engine)?:

    - When you kill the engine, the intakes will still have some remaining (un-burned) air-fuel mixture remaining in them. Upon powering up the bike (turning the key on), the ignition system will apply 12 volts to the coils, thus charging them. Of course, that constant current is not good for the coils, so a few seconds later (if the engine is not started) the TCI shuts down the coils by grounding them (to protect the coils from overheating) which cuts the current to the coils and thus triggers a spark to the plugs. If there is enough un-burned fuel in the intake manifolds or the combustion chambers, and if the valves are held open by the camshafts, a backfire thru the exhaust header and/or thru the intake manifolds/carbs/airbox can result.



    Why is my engine hard to start, and using the choke makes no difference?:

    Most probably, the starter jets --- which are tiny, and are down inside the carb bowl ---- are plugged up with fuel varnish or the like.



    Why does my engine run poorly (or is hard to start) after it is fully warmed up?:

    This could be due to leaking throttle shaft seals (where extra seal-to-carb body clearance occurs after the carbs warm up and expand), or, it could point to valve shim clearances that are dangerously tight (the clearances close up after the engine gets fully warmed up).



    Why are my plugs carbon-fouled (dry, sooty black deposits)?:

    - Carbon fouling is the result of incomplete combustion----for any reason. It is most often associated with an overly rich fuel mixture (whatever the cause), but can also be caused by an overly lean fuel mixture (or poor spark, etc.) In a lean-mixture condition, most of the un-burnt mixture gets pumped out the tailpipe, but some fuel droplets remain in the cylinder and add themselves to the next intake charge. That's not a very precise way of metering the mixture, so when it's finally rich enough for a spark to ignite, that particular charge may be too rich, resulting in incomplete combustion and plug fouling. So carbon-fouled plugs can be due to rich or lean conditions.......your Colortune spark plug will tell you for sure. If you have a light blue or white-ish flame, intermittent flame, and/or intermittent flashes of yellow within an otherwise white-ish flame, then your fuel mixture is too lean.

    And by the way.........if the spark that happens to ignite this overly-rich mixture is the "wasted spark" (which occurs in each cylinder at the top of the exhaust stroke, it will occur JUST AS THE INTAKE VALVE IS OPENING ---- so the backfire pressure wave may be directed back up the intake tract!



    Why are my plugs oil-fouled (wet, oily black deposits)?:

    - worn or broken piston rings, excessive wear or damage to cylinders, *leaking intake valve stem seals.

    * while bluish smoke from the exhaust can be caused by worn exhaust valve seals, that situation will not foul your spark plugs. Consider what happens: oil pools above the valve guides, and coats the valve stems every time they rise. These stem "seals" really aren't seals, they are more like wipers, and their function is mainly to wipe off the excess oil from the valve stem. Now, when these stem seals get old and hard, they leave an excess amount of oil on the valve stem, which then drops down into the path of the exhaust gas flow as the valve opens and the oil is evaporated off, leaving blue smoke from the exhaust. But note that none of that oil ever enters the combustion chamber, so it can't foul the plugs.

    Of course, any excessive oil coating an intake valve stem will end up going through the cylinder, but intake valve stem seals rarely fail on these engines. Unlike the exhaust valves, which are constantly baked by superheated exhaust gas, the intake valves are bathed in cool and moist (with gasoline) air.



    Why is the inside of my carbs covered with a brownish-green goo?:

    When fuel mixes with water and sits around for a while, this is the result. Nasty looking, nasty smelling, and you can bet that the tiny passages inside the carb body are plugged solid with this stuff! Definitely time for a full rebuild.......




    What are my fuel levels supposed to be?:

    Here's the Holy Grail on this subject:

    http://www.xj4ever.com/setting fuel levels.pdf

    And here’s a good visual guide to some problems that you might run into:

    http://www.xjbikes.com/forums/threads/setting-the-floats-mikuni-not-gettin-any-readings-fixed.40395

    and here’s a wonderful video from TurpentyneTV that shows the whole process in excruciating detail:





    Fuel Level Cheat Sheet:

    Here's the proper fuel-level settings by model when using the "clear-tube" method of measurement:


    Hitachi all HSC32 series models:

    NOTE: all of the following models used HSC32 carbs:
    XJ650 Maxim, Midnight Maxim, XJ650RJ Seca (non-turbo), XJ650 Euro all use HSC32 carbs (various versions)
    XJ750 all USA 1981-83 models use HSC32 version 5G200 (Seca) and 15R00 (Maxim and Midnight Maxim)
    XJ750 all Canadian 1981-83 models use HSC32 version 5H200 (Seca) and 15T00 (Maxim and Midnight Maxim)
    XJ750 UK/Europe 11M models, XJ750 Police models 24L and 37H use HSC32 version 5N100

    -Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)

    -Float height: 17.5 +/- 0.5mm


    Hitachi HSC33 series (XJ700 air-cooled models):

    -Fuel level measured via the clear-tube gauge: 1.0mm +/- 1mm (.039" +/- .039")

    -Float height: 16.0 +/- 1.0mm


    Hitachi HSC33 series (XJ750E-II model):

    -Fuel level measured via the clear-tube gauge: 5.0mm +/- 1mm (.197" +/- .039")

    -Float height: unknown


    Hitachi HSC33 series (XJ750RL models):

    -Fuel level measured via the clear-tube gauge: 1.0mm +/- 1mm (.039" +/- .039")

    -Float height: unknown, but possibly the same as XJ700 air-cooled models (16.0 +/- 1.0mm)


    Mikuni BS28 (all XJ550 except 1984 XJ550L):

    -Fuel level measured via the clear-tube gauge: 2mm +/- 1mm (.08 +/- .039 inches)

    -Float height: 21.5 +/- 1.0mm


    Mikuni BDS26 (USA all 1992-98 XJ600 Seca II):

    -Fuel level measured via the clear-tube gauge:
    USA: 4 - 6mm (.016 - 0.24”) below float chamber line

    -Float height: 6.2 - 8.2mm (0.24 - 0.32”)


    Mikuni BDST28 (non-USA all 1992-98 XJ600 Seca II):

    -Fuel level measured via the clear-tube gauge:
    1992-96 Canada and Australia: 3 - 5mm (0.12 - .0.20”) above float chamber line
    1992-95 UK: 3 - 5mm (0.12 - .0.20”) above float chamber line
    1996-98 UK: 8.5 - 9.5mm (0.34 - .0.37”) above float chamber line

    -Float height:
    1992-96 Canada and Australia: 11 - 13mm (0.43 - 0.512”)
    1992-95 UK: 11 - 13mm (0.43 - 0.51”)
    1996-98 UK: 8.8 - 10.8mm (0.35 - 0.42”)


    Mikuni BS32 (all XJ550L, 1984-85 FJ600, and 1984-87 / 1989-91 XJ600):

    -Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)

    -Float height: unknown


    Mikuni BS30 (all XJ650 Turbo):

    -Fuel level measured via the clear-tube gauge: 2mm +/- 1mm (.08 +/- .04 inches)

    -Float height: 17.5 +/- 0.5mm


    Mikuni BS33 (all XJ700-X and XJ750-X):

    -Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)

    -Float height: 17.5 +/- 1.0mm


    Mikuni BS35 (all XJ900RK/RL):

    -Fuel level measured via the clear-tube gauge: 5mm +/- 1mm (.20 +/- .04 inches)

    -Float height: 22.3 +/- 0.5mm


    Mikuni BS36 (all XJ900F, FN, N, etc):

    -Fuel level measured via the clear-tube gauge: 5mm +/- 1mm (.20 +/- .04 inches)

    -Float height: 22.3 +/- 0.5mm


    Mikuni BS34 (all XJ1100 and XS1100):

    -Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)

    -Float height:
    25.7 +/- 1.0mm (1978-79 all models)
    23.0 +/- 0.5mm (1980 all models)
    not specified (1981-82 all models)
     
  10. jjcurtiscb

    jjcurtiscb Member

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    Thanks Chacal! I do have a couple of other ideas to check before I completely throw in the towel.

    EDIT: I think I figured it out! The choke was partially stuck open because of too much tension in the line. Took it for a short spin with the needles 1 turn out and seemed to do alright. need to resync and see where I go from there! Think I am also probably going to get new plugs just to be safe.

    Thanks for everyone's help!
     
    Last edited: Apr 11, 2020
  11. jjcurtiscb

    jjcurtiscb Member

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    Well, I had it running. Ran great for about 30 miles, then ran low on gas after a full speed run. after that, it went to shit again and i cant seem to get the carbs synced. I adjust the screws and they seem to be dialed and then I put the tank back on and I get a super high idle again. I don't get it.
     
  12. Simmy

    Simmy Well-Known Member

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    Is the tank pinching the throttle cable?
     
  13. jjcurtiscb

    jjcurtiscb Member

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    I dont think so, but I did notice the choke cable was getting pulled too tight when turning because it was zip tied with the other cables. Hoping that helps but who knows. This bike is making me age quickly
     

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