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Need help 85 xj700 carbs

Discussion in 'XJ Technical Chat' started by Spitfrog, Jul 21, 2021.

  1. Spitfrog

    Spitfrog New Member

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    I had my carbs rebuilt but only dropped the carbs off not the bike, now I’m trying to put them back on and I’m having trouble. I would greatly appreciate some advice,tips/diagrams/pictures.. having trouble remembering where all the hoses go and having trouble connecting the choke cable. Thanks in advance for any help!
     
  2. tabaka45

    tabaka45 Well-Known Member

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    Getting them on for me is much easier if I push the air intake boots back into the air box. Also loosening the air box screw will allow it to slip back a little. I haven't done it, but removing the battery and battery box may let the air box go back further. I put some silicone grease on the intakes and then start with one side and try to work them on from side to side. A wooden board or hammer handle also helps force them on. If someone doesn't post a picture of the choke cable I can probably send a copy of the tech manual I have on my work computer. As far as all those hoses, mine mine are routed down the brake side of the engine.
     
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  3. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    Here is a picture of what I believe to be correct routing of the vent hoses. The #1 hose is a little bit longer. They all end up going down between the air box boots. This bike is currently disassembled, but once I get it back together I could take more photos if needed:
    20210518_024421618_iOS (2).jpg
     
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  4. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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  5. Huntchuks

    Huntchuks Well-Known Member

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    Route them below the bracket so they don't initially point up hill. It will look better too.
     
  6. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    @Huntchuks - the #1 vent hose has its own special little clip. After it goes through the clip, should it go up and over the #1 air box boot, like I have it in above photo, or underneath?
     
  7. Huntchuks

    Huntchuks Well-Known Member

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    What bike? My XJ700 carbs have two drain hoses, one between carbs 1 & 2 and one between 3 & 4.
     
  8. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    1985 XJ700N. I think these might have more vent hoses than the XJ700S.

    On the XJ700N, there are the two fuel overflow drain hoses, one between #1 and #2, and one between #3 and #4, just like the XJ700S.

    In addition there is a vent hose that comes off near the top of each carb on the XJ700N which I don't think exist on the XJ700S. So the XJ700N has a total of 6 "hoses to nowhere" hanging off the back of the rack.

    What you see in my photo above is the vent hoses that are routed over the rail for #2, #3, and #4, along with the #1 vent hose in the clip on the outside of #1. The fuel overflow drain hoses are below the rail.

    I'm still not 100% sure what the correct routing for the XJ700N's rats' nest of vent hoses, but I think I'm close.
     
  9. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    A little further investigation. From http://xj4ever.com/catalog/c-fuel.html:
    All 1985 XJ700 non-X (air-cooled models) and all XJ750RL models with the original HSC33-series Hitachi carbs also use four sections of 6.35mm fuel line, on the short brass vacuum port coming off (horizontal and angled towards the rear) of the front left of each carb body. Be aware that these hoses run from those brass ports to "nowhere"; that is, their other ends are merely open-vented to the atmosphere. These hose run from the vac ports, and are routed "upwards" and rear of the carb rack, and their open end rests below on the airbox. The #1 and #4 carb hoses are captured by a small bright plated clip, attached to the upper rack bracket outer screws, kind of "hidden" behind the bright carb end covers. On the #1 carb, this hose is approximately 9-1/2” long, while on carbs #2, 3, and 4 the hoses are only 7-1/2” long. All 1986 XJ700 non-X (air-cooled models) do not have these brass vacuum ports, and thus do not use these hoses.
     
  10. hogfiddles

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

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    Huntchuks—yours is an ‘86, so you do not have the 4 upper individual ones
     
  11. Huntchuks

    Huntchuks Well-Known Member

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    Well...that explains it.
     
  12. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    Here is an example that I found on an XJ700N for sale on cycle trader.

    On this one, you can see the #1 vent hose coming out from behind the chrome side cover on the carb, and then going up and over the #1 airbox boot.
    hose1.png
     
  13. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    All of the above research is correct. Additionally, California models (both 1985 and 1986 models....and this applies to both the Hitachi carbs for the air-cooled models and the Mikuni carbs for the water-cooled models) has an additional vac port on the #2 carb body, it's a much larger (fatter) port, and which points straight "up" (towards the sky) and is located just to the left of the pilot mixture screw.......this vac port is for the emissions control vapor cannister, located behind the right side plastic frame cover.

    Thus on 1985 air-cooled Cali models, you actually have a total of 7 (seven!) vac hoses ---- not counting the petcock vac hose --- the two bowl overflows, the 4 carb ports discussed above (whatever their purpose is; I don't think anyone is sure), and that emission cannister hose. Whew! Vacuum hose must have been cheap back then.

    Thank goodness that non-Cali air-cooled models only had 6 hoses..............:)

    ALSO----and I can't remember, my memory is hazy and my notes are fuzzy---I think (but ain't shure....) that when vac-synching these 1985 XJ700 airhead carbs, those 4 vac ports (not the bowl overflow, and not the Cali-only emission cannister hose) should be capped off (much like the intake manifolds are capped off) in order to get proper readings.

    In fact, I think you can run with these ports capped off all the time, but again----not sure. I think user @tabaka45 had some experience with this subject, and it may be his experience that resulted in my recollections above (but, maybe not)......
     
  14. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    I'm going to need to do a sync on my XJ700N soon. It would be good to know if those ports need to be capped.

    In addition, would they also need to be capped to do a colortune?
     
  15. hogfiddles

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

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    Dan, you don’t need to cap those. I have never needed to cap those when syncing or colortuning
    ADDITIONALLY, the line that goes into the canister is not the end of that line...... there is a line OUT of the canister that goes to a fitting on the underside of the CALIF tank. THAT fitting connect to a tube inside the tank where the vapors are released. Those vapors stay in the tank because the cap is a NON-vented cap.
    Whew——
    If you want to see the canister and/or the fitting on a tank, let me know..... I can show both.
     
  16. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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  17. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    I'm not sure that is how the system works while the engine is running, although when the engine is off that may be the operation.........I may be wrong, and I don't have a Cali tank here to experiment with, but...........the hose the runs from the carb to the emissions cannister (which is filled with charcoal) is providing suction (not pressure) to the cannister, and this suction also manifests itself inside the tank (via another hose from the tank to the emissions cannister). In other words, (vacuum) suction from the carb is being passed from the carb into the fuel tank, where gas vapors are evacuated. The emissions canister is also ported to atmosphere, and thus sucks in clean air, too. The fuel tank also has an "anti-rollover" valve (basically a one-way valve) that prevents fuel from exiting the tank should the bike fall over.

    This is my understanding of how it works, and I may be wrong. Note that there is no explanation(s) that I have ever found within the Yamaha service or owner's manuals in regard to this system (at least in the XJ700 manuals), but the same system was used on FJ600 Cali and YX600 Cali (and perhasp FZ600 Cali models) models --- so if anyone has one of those factory manuals, perhaps they are more explanatory. The Clymer FJ/YX/FZ600 manual has a slightly more coherent illustration than the XJ700 manuals do, as they provide "flow arrows" that illustrate the movement of fluids/vapors within the system, and it shows that vapors are being evacuated OUT of the tank, into the cannister, and then back out of the cannister into the carbs (again, via the suction provided by the #2 carb).

    The only problem that I have with my theory is that the suction of outside air into the #2 carb would seem to make that cylinder run very lean; but maybe it is somehow regulated inside the cannister, either by physical means (a jet of some sort) or that the fuel/air mixture coming into the #2 carb via this system is "close enough" to neutral as far as fuel mixtures are concerned, and any small difference is "adjusted out" during the synch process.

    BTW, I also don't understand why the 1985 air-cooled carbs had those 4 vac ports (Cali and 49-state carbs; i.e. "all of them") and what their purpose is. The bowls are vented via the t-fittings between each set of carbs (if those are overflow ports, then they are also an atmospheric port for bowl venting), so I'm not sure why they appeared in 1985 and then disappeared in 1986. If anyone can shed light on this mystery, please do!
     
    Last edited: Jul 28, 2021
  18. hogfiddles

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

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    Interesting to consider the flow going the other way— that makes sense, too. I though the flow was to vent fines to the tank, not the atmosphere. Opposite flow would ‘vent the fumes to the carb to burn though, however, fuel would flow that direction in the even of a roll over then...... I think.
    Maybe I’ll see if the valve can come off so I can investigate flow direction more
     
  19. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    I'm pretty sure the "anti-rollover" valve is a simple one-direction check valve, and it prevents fuel (but not vapors) from exiting the tank when the tube (inside the tank) is immersed in liquid fuel....which of course can only happen when the tank is on it side, or greater. I think that it will pass vapors in either direction (which keeps the tank from vapor locking), or, the Cali fuel cap allows air IN but prevents it from escaping.
     
  20. VanDutch

    VanDutch New Member

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    Hi Guys,

    I just bought a 1986 XJ700 and bike was leaking gas, ran for a second then died and lots of gas leaked out of the Air filter box. Bought it as I thought easy fix???

    Anyway took it home pulled the carbs and they were so gummed up and believe the guys never had them cleaned 11 k on bike.

    Anyway I cleaned them put them back on and for the life of me do not know where the vacuum hoses go. I know on goes from carb to to vacuum on petcock but the other two larger one no clue. I don think they were hooked up or parts missing. The bike runs really rough and barely stays running. So I hoping when I get vacuum lines resolved I can get it to idle etc.

    Does anyone have a vacuum hose routing. I see two larger ones, I know small #2 vac goes to the petcock but dont get where the other two go? Im I missing a tee connection as well?

    Any help for this old Namera vet would be appreciated

    Kind regards,

    Dutch
     

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