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New to forum and carb questions

Discussion in 'XJ Technical Chat' started by Loveland'81, Jul 1, 2019.

  1. Loveland'81

    Loveland'81 Member

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    Hello everyone! Brand new to the forum and the XJ line of bikes. I bought a used 81 XJ 650 a few weeks ago and I have been going through the entire bike. I have yet to hear the bike run because I want to get everything sorted out first. It was in pretty bad shape and so many things were backwards or wrong with it from PO. I am slowly working it out. I have cleaned and separated the carbs, new throttle shaft seals ( thanks x4forever!), jets etc. The problem I am having is the carbs were originally attached to a 750. The jets were for a 750 so obviously larger sizes. Ive already replaced the main and secondary fuel jets and needles etc back to stock recommendations for the 650. The pilot air and secondary are 225 and 80 that are in there now. My concern is how well it run with the larger jets. Could I just color tune it and move on? Are those air jets only used for idle mixture? All of the other jets , compensater and other fuel jets match with the 650. Thank you so much all and I look forward to a long membership!
     
  2. k-moe

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

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    The larger air jets will lead to a hanging/runaway idle. and a lean mixture at higher RPM.
    There is one air jet for the pilot, and one for the main.

    Be aware that the diagrams in all of the service manuals hae the positions of those jets mislabeled.
    The photo below is correct.

    [​IMG]
     
    Last edited: Jul 1, 2019
  3. Loveland'81

    Loveland'81 Member

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    Thanks for the info kmoe! Ok, ill track down the 195 and 50 air jets I had no idea they had that much influence. That would drive me crazy.
     
  4. XJ550H

    XJ550H Well-Known Member Premium Member

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    carb jet specs
    http://xjbikes.wikidot.com/carb-specs

    do not know if this will be an issue do not quite understand this part on carbs yet
    81 xj650
    Main jet NEEDLE ID: #Y-12

    81 to 83 XJ750
    Main jet NEEDLE ID: #Y-13
     
  5. k-moe

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

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    It would be an issue, but he already changed them. Different jet needles change the rate at which the fuel to air ratio is adjusted as the slides lift.
     
  6. Loveland'81

    Loveland'81 Member

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    Thanks all. I will be sourcing air jets through xj4ever. I have a new problem i just discovered. This bike was Frankensteined in a bad way. Originally titled as a 750 82 xj the po installed a 650 motor instead of a 750. Additionally after research its not a YICS and is an 81 maxim engine. The 750 tci is in place so i have no idea if that will work with a non yics engine. Any experience with a 750 yics tci on a 650 non yics? Im trying to source an 4h7-10 tci but having issues finding one. Thanks everyone for help!
     
  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    the nonyics has differert timing in its tci but yics 650 and 750 are the same

    did you id the motor as seca or maxim 650?


    you are looking for green label tci.

    there are also black lable tci for the 650 I think it was used on the midnight 650 do not know if it matters
    I have a black label tci from a 650 midnight maxim

    I was going to buy a midnight motor but got out bid at last moment and had already purchased a black label tci from another midnight.
    side note they will all start and run the 650 or 750 motor

    there is a thread/discussion on black tci someplace.
     
    Last edited: Jul 1, 2019
  8. Loveland'81

    Loveland'81 Member

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    It seems to be a maxim engine from the serial number but I am not 100% sure. The number plate on the engine is 4H7-004330. I managed to find one on ebay ( black label) so hopefully that is the correct box. I can only imagine how terrible this bike ran before i got it.
     
  9. XJ550H

    XJ550H Well-Known Member Premium Member

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  10. Loveland'81

    Loveland'81 Member

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    Thanks XJ for confirming. Things are slowly getting there after sourcing parts. Just about done with carbs they were a mess.
     
  11. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Actually, the 650 non-yics and the 650 yics/750 TCI's use the same advance timing, the only difference between the 2 boxes is the inclusion of a grounding pin for the sidestand safety circuit on the '82-up (650 yics/750 all) models. The non-yics box is the 4H7-10 black label version, and the yics version is the 5G2-10 red labelled box.

    The green label box (5V2-10) is for the XJ650RJ Seca (non-yics) versions, and its timing is slightly different. The 650RJC Canadian Seca models got a yics engine, and thus uses the 5G2 box.

    The 5G2 (yics) box will work just fine on the earlier XJ650 non-yics engines...…….it has an extra grounding pin which isn't going to be hooked up to anything. Note that the reverse situation is not true.....using the black-label 4H7 (non-yics) box on a 650 yics/750 engine will allow the engine to perform the same (since they have the same advance curves), but you'll lose the sidestand safety feature (which is something you definitely want to have!).

    And just to clarify: the difference between the black-label 4H7-10 and the red label 5G2-10 tci boxes is not due to any advance/timing differences, it is only due to the use of the grounding pin on the 5G2 boxes...…...the 1980-81 XJ650 Maxim/Midnight Maxim models did not use a sidestand switch/relay/safety feature, and thus no grounding pin (to disable the TCI under certain conditions, i.e. "the sidestand is down" safety feature) on that earlier 4H7-10 tci box.
     
    Last edited: Jul 3, 2019
    k-moe, Franz and XJ550H like this.
  12. XJ550H

    XJ550H Well-Known Member Premium Member

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    thanks for clearing that up
     
  13. Loveland'81

    Loveland'81 Member

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    Thanks for the info chacal! I ended up ordering one from eBay ( black box ) so apparently I didn't need it after all. Ill try to resell it, The red label is on the bike now (5G2) I will leave it in place if the advance is the same. Its not been fun reworking things as I mentioned the PO put a 650 engine when originally it has a 750 in it. I have had to swap jets, buy related parts etc. Excited to hear it run for the first time and correctly. I am also wondering if the tach will work still since it had the Atari cluster in it. The 650 motor has the mechanical tach output on the front so I am not sure if the tach will still work. Apparently its connected to the coil so I would think it would. The original 750 main wiring harness is still on the bike.
     
  14. k-moe

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

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    The tach will work so long as it's connected (and in working order).
    Chacal sells a blanking plug for the mechanical tachometer port if there's not one there already.
     
  15. Loveland'81

    Loveland'81 Member

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    Thanks everyone for your help. I got the carbs completely rebuilt, throttle shafts fuel o rings cleaning everything. Put them on bike and sync and color tuned. Idled decent but I had to play around with the control knob to get a steady idle. When I rev it up it hangs and takes a bit to come back to idle. I also adjusted the valves. The bike falls flat on its face at 5k rpm and sputters. It seems like it looses power. One thing to note is that there is a small fuel filter attached to the output of the petcock. The bike also has a manual petcock installed. I checked the boots with starter fluid and didnt find leaks. Could this be a bad coil issue? I am also having an issue on restart after its ran for 5 or 10 minutes. The starter turns over slowly and takes an extended crank to get it running again. Any help would be greatly appreciated thanks everyone.
     
  16. Simmy

    Simmy Well-Known Member

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    Do you have an air box?
     
  17. Loveland'81

    Loveland'81 Member

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    Yes, I had to buy one because it originally had pods. Put on the correct 650 air box and boots are good all the way around. I had a few things out of sort so its gotten better. I am still having a slow to return idle. Spark plugs are perfect brown. Sync good, new spark plugs and caps. The slow to start after warm was due to a bad battery it wasnt charging. Put a new one in and its charging well and starts good when hot now. I also have some dyna coils on the way.
     
  18. XJ550H

    XJ550H Well-Known Member Premium Member

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  19. Loveland'81

    Loveland'81 Member

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    Ok all I am still having issues with the bike. I still get a hanging idle and slow to return to idle. Also I cannot get the bike to rev past 5,000 rpm under load. Wide open throttle it doesn't budge past 5k and just sputtered. It will go to redline not under load. I rebuilt the carbs with all new seals including the throttle shaft seals. Carbs are colortuned and syncd. Just finished putting dyna coils and new spark plugs in. Inline filter is clean and flowing well. What else can I check? I do have the stock airbox and filter installed. Thanks
     
  20. XJ550H

    XJ550H Well-Known Member Premium Member

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    color tune and sync after shims done? if not re sync carbs and color tune.
    did you wet set fuel levels of just set floats to 17mm I think?
    do all exhaust pipes get hot and equally hot or do you have a colder pipe?

    air jets in correct location? you can check this with carbs on bike.

    idle must be adjusted after riding bike for 10 or 20 miles not in your drive way after a cold start.
     

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