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Carb rebuild!! Losing my sh#$%.

Discussion in 'XJ Technical Chat' started by Joshua Olkowski, Sep 10, 2018.

  1. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    ....and I've only ever had to use a strap one time, and a hammer handle one time.........
     
  2. Joshua Olkowski

    Joshua Olkowski Member

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    Well guys. My attempt was overall unsuccessful. I finally got the carbs on the bike. My hands are completely raw and swollen getting those boots on but I did it. Anyway, I hooked up the gas tank and let fuel ease on down only to see it leak back into the airbox. Noooooooooooo. I'm not sure why that happen. I replaced all the O-rings to the valve seats and checked float heights, ect. I checked for leaks by filling the carbs up with gas before I put them on the bike. Everything was fine. In any case there was still gas in there so I attempted to start the bike anyway and now I'm not even getting spark. Again, don't know why that's happening. I fully charged the battery before installing it. What do you think? Sledgehammer time?
     
  3. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    No, we just have to work methodically through things......

    It's not uncommon for the needles to get. Bound up a bit while working on getting the carbs in. Usually. Few raps with a screwdriver or hammer handle jostle them enough for the fuel to get them to up into the bores properly.

    The no-spark issue has nothing to do with the fuel. That's electrical
     
  4. Joshua Olkowski

    Joshua Olkowski Member

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    No spark issue has been resolved. Bike started right up, however, it's not all fine and dandy...yet. Unfortunately, a fuse blew. Not exactly sure why that happened. Anyway, I was able to turn on the bike on and play with it for about 20 minutes. The bike now runs worse then before. To my credit though, I haven't been able to adjust the mixture screws and who knows how accurate my bench synching skills are. So, the idle is a little rough and the choke seems to only go on, or, off. I can't do half choke. What really concerns me, though, is that the hanging idle is still happening, however, it's different. It will hang up for about 2 seconds but then all of sudden goes down like something is caught and then releases where as my last hanging idle problem was that it would hang up for maybe a second but SLOWLY come back down. I bench synched for an hour to get it as evenly accurate as I could. I currently have all the mixture screws out at 2.5 turns. It also seems like the idle knob is close to being all way in because it's very hard to turn. Does anybody have any suggestions on how to proceed at this point?
     
  5. wibblee

    wibblee New Member

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    I'm new to the xj game, so I might be able to help you from a "I don't know what the hell is going" on point of view.

    I made the mistake of not labelling my butterflies. They were not perfectly interchangeable between carbs. Spent a few minutes fixing that mistake.

    I used the throat hole method of bench syncing. Look it up. You bench sync according to the little holes in the throat of the carb instead of using little strips of paper or whatever.

    But right now, I'd recommend making the homemade carb sync tool with two jars and giving it a try. I thought my bench sync was pretty damn good, but carb syncing while running showed it was still off.

    The first time through feels like a job, but soon it's no big deal to get in and out of them. Good luck!
     
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  6. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    1. Bench sync takes less than two minutes to do.

    So even as a newbie, if it's taking two hours, you're doing something way wrong.

    With a homemade sync gauge of only two jars, you're gonna have nothing but frustration. I highly recommend getting the Morgan carbtunePro. Learning curve is about Five minutes.

    If the idle knob it all the way in, you should racing to beat the band.

    If you wish help, I do offer rebuild services.... if you want to pull the rack and ship it out to me, Ill look it over and get it set back up the way it should be.

    If you send me a private conversation, I can talk with you more...

    Dave Fox
     
  7. Paul Howells

    Paul Howells Active Member

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    @Joshua Olkowski
    Are your bowls still overflowing into the air filter housing? Or did you get that resolved. Did you set the float levels when you did your rebuild?

    There are a number of reasons why your bike will be running poorly right now. You need to be methodical with the steps you take to get it all tuned up. The gurus may have some other ideas but here is my suggestion:

    1: Check and adjust the fuel levels in your float bowls. If you have the manual there will be instructions for this. There are also many posts on this site. This is important especially considering the overflow problem you described.

    2: Test your coils and replace your plugs.

    3. Set all your idle mixture screws to the factory defaults. 2.5 turns

    4. Set your idle adjustment screw so it is just touching the throttle. Start the bike and warm it up while you adjust the idle enough so that it will idle on its own. If you cannot get it to idle at this point it is likely that you have a vacuum leak. Make sure your intake boots are seated correctly and nice and tight. Check your hoses. There are lots of posts on finding vacuum leaks. If it still won't idle once a leak is eliminated then your bench set may be way out of whack.

    5. Beg, borrow, build or buy a sync tool. This is something it pays to throw a little money at as it will save you time and frustration knowing your gauges are working properly. Syncing your carbs will resolve many issues that you may think are unrelated.

    6. Adjust your idle fuel mixtures. There are a few ways to do this. Most people on this site recommended using a Gunson Colortune. Worked for me. Make very small adjustments.

    7. Repeat steps 5 and 6 until you are satisfied with your performance. If everything is stock on your bike ( including jets and air filter) then this should work for you barring any undiagnosed issues with the ignition.
     
  8. Mic

    Mic New Member

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    Joshua, did you ever get this sorted out with your carbs? Curious, I have had my carbs out 6 times in the last couple months, definately a tough one to deal with. I am in So. Cal
     
  9. Joshua Olkowski

    Joshua Olkowski Member

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    Awesome. Great list. Thank you kindly. Could you direct me to a video about building a synch tool or recommend one to buy? Thanks.
     
  10. Joshua Olkowski

    Joshua Olkowski Member

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    So, the carb rebuild is finished and it is, I believe, a success. I hoped doing a carb clean would fix every single problem on that bike but there has indeed been one consistent little problem that I've been ignoring...a hanging idle. Keep in mind that after doing the carb job I discovered there was nothing really wrong. Every orifice was clear. So, I believe I did not need the carb job in the first place but I'm glad to have done it. In any case I may start a new thread for this but I'll present the problem here first: So if you can indulge me and believe that my carb job was successful, what are some reasons for a hanging idle? When the bike is turned on the idle is fine but right after opening the throttle it will rev to about 4ooorpms and just stay there...almost like the choke is constantly on. You can bring down the idle by being in gear and letting the clutch out just enough before the bike needs to move. You can also kind of ghost the kill switch and that brings it down too. I checked the choke and between me and my friend we determined the choke was working fine. The bike always had this problem and I was hoping it was a carb issue but I believe it may be something else. Ignition/timing issue maybe?
     
  11. Joshua Olkowski

    Joshua Olkowski Member

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    I think I did. Unfortunately, I'm still dealing with a hanging idle problem but I have yet to take the time to adjust the idle screws. I bought a Gunson color tuner and I'm going to wait for that in the mail before proceeding. I'm really hoping I don't have a valve or timing issue but I'll keep you posted. I agree, tough one to deal with.
     
  12. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Have you done a running (vacuum) synch on the engine? If not, stop doing any/everything else and perform that procedure, otherwise you'll chase your tail until the cows come home and, most likely, throw every adjustment imaginable off in doing so. And, check the fuel levels in the bowls and fix if necessary.
     
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  13. Joshua Olkowski

    Joshua Olkowski Member

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    I'm a beginner so please explain to me what a running synch is like I'm a two year old.

    I'm awaiting a Gunson Color Tuner. Will that tool help me with what you're talking about. I also bench synched as much as I possibly could to get them into synch.
     
  14. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Engine Tuning Tools:

    j2) Aftermarket Morgan CARBTUNE PRO 4-COLUMN SYNCH GAUGE TOOL.......brand new, no display box, includes all accessories and instructions. This is the one that professionals use and recommend, and is superior in design, ease of use, and accuracy versus vacuum gauges and all other versions, whether fluid-filled or otherwise. Uses damped stainless steel sliding dowel rods instead of mercury or the "blue mystery fluid", giving accurate, safe, and easy-to-read measurements. More expensive than other synch tools and worth it. Use it even once and you'll wonder how you lived without it.

    NOTE: this tool is used on all XJ engines, regardless of whether it is a "YICS" engine or not, and is necessary to perform the “running” or vacuum synch. If your carbs have been removed from the engine for a rebuild, then it is also suggested that a “bench synch” procedure be performed, which does not require this (or any) tools perform….the only purpose of the bench synch procedure is merely to get the carbs set up “close enough” to allow the engine to start and run, at which time a running (vacuum) synch of the engine should be immediately performed, using the HCP96Q synch gauges, A great visual guide to the bench synch process can be seen at:

    http://xjbikes.com/forums/index.php?threads/6366


    Please note that Yamaha specifies that the engine synchronization procedure should be performed every 2,500 - 4,000 miles to insure the maximum performance and life-expectancy from your engine.

    Also, please note! you can sometimes find these same sticks selling at a discount at various places, but most of these places are offering a much older, now-discontinued Carbtune II version, rather than the latest, much-improved Carbtune PRO version that is offered here. The PRO version is much more durable, accurate, and easier to clean and service than the older version.


    Here's a great tutorial on using the Carbtune Synch Gauges:




    The Colortune Plug will help in adjusting the pilot fuel circuit mixture screws, but that is all it is used for. The engine synch is equally important, and, it should actually be used in conjunction with a set of synch gauges.



    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......



    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:

    - 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/



    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)




    Question #2: What Parts Will I Need?:

    The parts you'll need depends on what is there, what is missing, what is worn out, what gets broken or damaged during the dis-assembly process, etc., but the "basic items" needed for the rebuild process (besides any special tools and tuning equipment) is as follows:

    - throttle shaft seals (you'll have to split the carbs from the rack to replace these).

    - fuel supply tube o-rings (you'll have to split the carbs from the rack to replace these) on the models that use them (some Mikuni carbs do not use these).

    - float valve needle and seat rebuild kit (seat, needle, clip, seat washer. The float valve seat filter screens are also available separately). Mikuni owners will also want to replace the float valve seat o-rings.

    - float bowl gaskets.

    - idle mixture washers & o-rings for sure, and the idle mixture screw springs and mixture screws if they are damaged.

    - jets, if damaged or incorrectly sized.

    - carb bowl fuel drain screws, if damaged.

    - new replacement carb hardware (screws, etc.)---now is the time to upgrade to stainless steel and/or allen-head fasteners if so desired!



    From Our Experience:

    Since the carburetors are THE most troublesome (and thus most expensive) aspect of these bikes, let me offer a few dozen words and insights about them, their service, and expense:

    These carbs are quite simple, mechanically speaking.

    The process of making DARNED SURE that you get them unbelievably, positively zestfully clean is a matter of stick-to-it-ness and resisting all attempts to take "shortcuts" or to brush off the tedious aspects of it. Many of the passages in these carbs are tiny, and it's that "tiny-ness" that bites most people, as they don't want to or don't realize the amount of effort that has to be undertaken to deal with such small passages.

    If you read through these forums, you'll see many tales of woe of people who are now "cleaning" their carbs for the 2nd, 3rd, or 4th time BEFORE they get it right. The problem is, they never really "cleaned" them correctly the first, 2nd, and 3rd time. After all of the frustration and hassle involved, by the time they get around to the 4th go-around, then they understand that when people who have SUCCESSFULLY rebuilt carbs say things like "you'd better make SURE that you get clear flow through each and every passage, and you'd better polish that piston diaphram bore", etc. aren't just saying that to be over-the-top retentive about their own habits and style of working on these carbs, what they're really doing is issuing an experienced WARNING: do it right, or keep doing it again, and again, and again. And although they're kind of fun little critters to play with, taking them all apart and putting Humpty Carby all back together again, well, it's time better spent on other things.


    Think we're kidding? The following thread is a "must read", because the title says it all:

    http://xjbikes.com/forums/index.php?threads/17821



    One last note: "cleaning" the carbs (internally, not just making them look pretty on the outside) is just one of the small subsets of tasks necessary to the proper REBUILDING of the carbs. I cannot stress this point enough. The use of the term "cleaning" is used as if it were the end goal of the process; in reality, the proper way to think about it would be this:

    "A complete and exceptional level of carb CLEANING is a vital and necessary part of the process of properly REBUILDING the carbs."

    And what are the other components of the rebuilding puzzle?

    a) getting the darned things off the bike! This might help:

    http://xjbikes.com/forums/index.php?threads/29695

    and

    http://www.xjbikes.com/forums/threads/made-a-how-to-video.103484/



    b) replacing the worn, missing, or necessary "wear parts" on the carb.


    c) Proper "service" work to the carb bodies, especially:

    - polishing the piston bore for silky smoothness.
    - repair or clean up of any stripped threads in the carb bodies.
    - replacement of any damaged or worn parts. In fact, the ability the recognize what is damaged and worn (besides the parts above which are designed to wear out) is the most difficult part of the entire task, since it requires a level of experience: are my needle tips worn? What, exactly, does a worn needle tip look like? How "smooth" is smooth enough? Etc. This is where the advice and experience of the members of this forum are invaluable.


    d) Proper "settings" of the various components during re-assembly:
    - the fuel levels (float heights).
    - the "basic or bench synch" of the throttle valves


    e) On-bike "settings":

    - first and foremost, the measurement and setting to specifications of the valve train (shim) clearances. Failure to do this "wastes" 90% of your efforts involved with the carbs.
    - final synch (using some type of manometer and the YICS tool if your engine is YICS-equipped)
    - idle mixture screw setting, preferably using a Colortune plug.


    f) A lot of useful "how-to" threads can be found at:

    http://xjbikes.com/forums/index.php?threads/27544

    and scroll down to the CARBS and FUEL SYSTEM: section........


    One last thought about these carbs, since they are THE most troublesome aspects of these bikes, and something to consider:

    - the four carbs concept is really neat looking, and is certainly performance-oriented to the extreme.

    - for many of us who had lots of experience with automotive carbs, just beware that while these Hitachi and Mikuni carbs are a bit different in operation (and thus parts), a carb is a carb, and they're pretty basic little devices. The main difference is that the fuel circuit passages on these carbs can get bizarrely tiny, especially if you're used to working on automotive carbs (which have canyon-sized fuel passages compared to these carbs).

    - like I've said, the cleanliness part is really just tedious work, with a couple of "tricks" thrown into the mix, given the small sizes you're having to deal with. The "rebuild" part is basic mechanical knowledge and skills, knowing which way to turn a screwdriver to loosen vs. tighten, when and how much force to use or not, being organized, stuff like that.

    - but the "tuning" part will require some special tools, but no type of any rocket-science knowledge or skills----once you master the rebuild and tuning process with these bikes, you are pretty much a Carb Tuning God, as these carbs are about as "complicated" as it gets with carburetors. I mean, VERY few vehicles have multi-carbs, not until you get to the really high-performance machines level in the automotive world.

    - well, as "complicated as it gets" until you start adding pods, etc.----which if you do, I sure hope you've got every last one of the basics listed above down to a science, and you can do it all, properly, and blindfolded, too!

    - finally, if you do not have a service manual(s) for your particular bike(s), and you're going to wrench on it and want to do things right, then the only thing I can surmise from such a course of action is:

    a) you're already an expert, or.....

    b) you aren't really serious about doing things right, and that's okay, too---just don't expect good, quick, or cheap results!



    The following guide may save untold hours of frustration and grief:

    http://xjbikes.com/forums/index.php?threads/14692
     
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  15. Paul Howells

    Paul Howells Active Member

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    @hogfiddles recommended the Morgan carbtunePro. I'd go with that. Check Amazon.

    Your hanging\runaway idle is caused by a vacuum leak or being out of sync so go through the list as I suggested.

    Old throttle shaft seals in the carbs can be the source of a vacuum leak and result in a hanging idle but you replaced those when you did your rebuild, right?
     
  16. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    The purpose of a BENCH synch is to merely get the throttle blades positioned somewhat equally (and at an appropriate opening) so that the engine can start up and run (even very poorly) on its own. If the bench synch accomplished that (which it did for you), then you were successful at that procedure, and it has outlived its usefulness and purpose. Once the engine is running, then you MUST do a running (vacuum) synch to get each of the cylinders producing an equal amount of output (hence their power output is "synched", which is what the word actually refers to). Engines which are out-of-synch are acting like four individual engines, each fighting along with (or against) each other at various times, and thus that is why an engine that is out-of-synch will exhibit symptoms of lean, rich, runaway idle, etc.....sometimes individually or changing with rpms, engine temps, etc........as the individual cylinders are fighting against each other for control of the entire engine.
     
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  17. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    P.S. we have the Carbtune Pro versions in stock, and once you use one (same for the Colortune plug) you'll never understand how you got by without it!
     
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  18. Joshua Olkowski

    Joshua Olkowski Member

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    I have no idea what a throttle shaft seal is.
     
  19. wibblee

    wibblee New Member

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    Josh, you have to read the stuff chacal posted. I know it seems like a lot, but it's all valuable to know. It's a one stop crash course of what you need to know.

    To answer your question, look for the section on why your bike is schizoid. It fixed the hanging idle on my bike. I used the #11 orings instead of seals. It's worked so far.
     
  20. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Throttleshaft seals are the little round seals on each end of the throttle shaft--the rod that has the butterfly fastened onto it. To replace them you MUST break the rack apart, remove the butterfly, disassemble the linkages completely so the shafts can be pulled out in order to replace the seals.

    If you don't know what they are, then you obviously have not rebuilt your rack. The seals are old, and most likely leaking.

    Here are 3 pics of a rack torn down for a rebuild. If you didn't go this far, you didn't rebuild. Period.

    image.jpeg

    image.jpeg

    image.jpeg
     
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