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Stupid question - which screw is for fuel adjustment

Discussion in 'XJ Technical Chat' started by MaximusXJ650, Jul 15, 2019.

  1. MaximusXJ650

    MaximusXJ650 Member

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    I've just had a brain fart where I've completely forgotten which screw adjusts the amount of fuel going to the engine via the carbs.

    I cant decide between the one under the brass plug or the bigger one between the carbs.

    Xj650 maxim.

    I'm running lean according to the colortune (giving a light blue color) so I dont know which screw to turn to make it more rich.

    I remember from setting the carbs up that i turned the screw under the brass plugs 2.5 turns out

    Thanks
     
  2. firebane

    firebane Active Member

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    The big one just works the idle. You will need to adjust the ones under the brass caps for the colortune.
     
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  3. k-moe

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

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    As above, the screws under the brass caps adjust fuel mixture. Since your caps are still in place the carbs haven't been properly cleaned since being sent to the dealership on the brand-new motorcycle (and the -orings are likely hardened and near-useless).

    The slotted screws between the carbs control the throttle plate synchronization.

    The big knob under and between #2 and #3 controls the idle speed.
     
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  4. MaximusXJ650

    MaximusXJ650 Member

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    They have been removed, I removed and refitted them during the carb strip down.

    I saw posts about drilling them out but I took a small thin flathead and prised them out with little to no effort.

    I'm having difficulty tuning in the left side of the engine. During the colortune process I cant seem to get that deep blue colour on #1 & 2 like I can on #3 & 4. It just stays a pale blue which I believe is lean.ė

    I've had the carbs apart again and checked the float setting both wet and dry and its spot on. I even made sure that the tiny hole in the float bowl was clear - if said hole was blocked what would it do?

    The bike runs and rides but bogs when opened full throttle and I cant get past 65mph.

    Losing hope with this, I just want it to run properly...
     
  5. firebane

    firebane Active Member

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    Valves adjusted? Stock Airbox?
     
  6. MaximusXJ650

    MaximusXJ650 Member

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    Yes and yes. Full carb strip down, new butteryfly shaft seals and fuel o rings. Been in a ultrasonic cleaner too
     
  7. k-moe

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

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    Pale blue will be fine, as long as the plug color doesn't show leanness and you don't get any popping on deceleration.
    There might be a small vacuum leak somewhere other than at the carbs. Worth checking out the intake boot base seals and the vacuum port caps to be sure.
    Check the plug color after a good long ride. Look for the color on the ground strap and base ring more than on the insulator. A light grey insulator is fine, but light tan is better. The ground strap should have a noticable change in color just about at the bend (indicating that the plug is reaching the self-cleaning temperature), and the base ring should be sooty all the way around, but not a dark black soot. The big tell for being too lean will be flecks of aluminum on the porcelan or ground strap. At that point the mixture is dangerously lean and needs to be made richer, or the underlying problem found and solved.

    The tiny hole in the bottom of the float bowl is the enrichment jet. If it were blocked you'd have difficulty with cold starts, and nothing more.
     
    Last edited: Jul 15, 2019
  8. MaximusXJ650

    MaximusXJ650 Member

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    I'll grab a picture of the sparks after work tomorrow.

    Would a small vacuum leak cause the lack of power post 65mph and the bogging down an lower revs on cylinders 1 and 2 (dependant on where the leak is)
     
  9. firebane

    firebane Active Member

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    Have you checked spark plug gap, spark plug cap resistance and coil resistance? Compression check?
     
  10. MaximusXJ650

    MaximusXJ650 Member

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    I'm not sure on how to check any of those. I've assumed compression is fine given that it runs. Coil resistance shouldn't play a part should it? No issues on startup
     
  11. firebane

    firebane Active Member

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    All super easy checks.

    Compression is a gauge you buy.. disconnect fuel and plug wires and remove a plug stick in tool, crank bike with throttle open till needle stops moving.. Compression on 1 side.

    Caps get a multimeter and check the ohsm through the cap

    Coils are a bit more to do but not much. You take off the caps and measure the ohm across the leads with caps off for primary and secondary.
     
  12. XJ550H

    XJ550H Well-Known Member Premium Member

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    disconnect tci when doing compression test. test is best when a car battery is used as bike battery will drain and starter will slow down
     
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  13. MaximusXJ650

    MaximusXJ650 Member

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    Are there any how to videos? I'm more of a visual learner Haha.

    I dont want to be spending more money, I feel I've already piled loads into it.

    If only it would run properly (sigh). Its fine for my work commute as I don't get past 40 but on the open road it bogs at full throttle.

    I read these bikes are easily capable of 80+ speeds - I've done so much work on it and I'm starting to feel defeated on the fuelling issue.
     
  14. k-moe

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

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    Have you removed the top hats and inspected the diaphrams for holes or cracks lately? They may have showed up since the last time you had the carbs off.
     
  15. XJ550H

    XJ550H Well-Known Member Premium Member

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    are all the exhaust pipes equally getting hot? be carful just slap each one see if any feel colder

    sounds like your running on 3 cylinders.

    use a meter and measure the resistance between spark plug cap 1 and 4 should be 21k ohms do the same thing for caps 2 and 3 again 21k ohms

    if you fail above step unscrew spark plug caps from spark plug wires retest spark plug wires.

    test spark plug caps from each end should get 5 k ohms

    what kind of plugs are you running?

    ends of spark plug wires may be corroded and may need to be trimmed 1//8 to 1/4 inch.

    in next step note wire positions.

    then go to the tci disconnect the 4 position connector and measure ohms from red/white wire to gray wire and red/white wire to orange wire looking for 2.5 ohms for each set plug it back in .
    meter set to 200 ohm or lower setting
    that completes the ignition coil test

    pick up coils
    then unplug 6 position connector read ohms from black wire to gray wire and black wire to orange wire see spec below
    then test black wire to ground you should get no reading

    plug connector back in testing done

    your specs
    XJ650 models:

    Pick-up coils:
    1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
    1982-84 XJ650 Maxim: 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range

    Ignition Coils:
    Primary side (input from main wiring harness):
    2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

    Secondary side (spark plug wires, without their end caps):
    11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range


    Spark plug caps:
    5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range

    Spark plugs:
    0 ohms per plug

    also run bike inside barn and look up under tank see if you have a light show going on from coils and wires
     
  16. XJ550H

    XJ550H Well-Known Member Premium Member

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    blue bunsen blue anything but white thats lean. do not get hung up on the pilot jets.

    if you apply a little choke do you get the color you seek or yellow?

    with choke off
    briefly bring rpm up over 3krpm 3500 rpm is good what color do you get?
     
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  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    are you sure air jets are in correct spots under the hats ? 80 goes near the screw hole.


    are any of your pilot jets swapped with the main jet? main jet has a washer under it and connects to emulsion tube under slide needle
    pilot is farthest from float.
     
  18. MaximusXJ650

    MaximusXJ650 Member

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    Thanks xj550h I'll be sure to give these suggestions a go tonight if I get chance.

    To check, when I'm doing the resistance checks, do I connect the red cable from the meter to red/white wire when checking 4 position cable and to the black wire when checking the 6 position?

    See picture for jet positioning:

    20190705_201317.jpg
     
    Last edited: Jul 16, 2019
  19. MaximusXJ650

    MaximusXJ650 Member

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    Just noticed this pilot is a 40 and the main is 110...

    But this is correct in accordance with the church of clean (I have a US import)

    Screenshot_20190716-071909_Chrome.jpg
     
  20. MaximusXJ650

    MaximusXJ650 Member

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    No I haven't although I can't see them having holes since I last put them in at the beginning of the month.

    I'll do xj550h suggestions as the bike would need to be started on some of them and if still no luck I'll check the diaphragm.
     

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