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XJ650K idle circuit running rich

Discussion in 'XJ Technical Chat' started by Jeff Witt, Oct 10, 2021.

  1. Jeff Witt

    Jeff Witt New Member

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    Looking for some advice on tuning. I've rebuilt the carbs and read all the posts about getting them clean. The holes for the idle jet in the bowl are clear (Carb cleaner sprays 10 feet out). I started with the idle mixture screws at 2.5 turns out its way too juicy there. I put in brand new plugs tuned the idle mixture down to 1 turn out from closed. I ride it around the block it idles like shit but as soon as I get into the needles it runs awesome pulls nice and hard but then when nt accelerating and it is back to the idle circuit it bogs and sounds like its being strangled. I pulled out the plugs and they are all black. I do not have a color tune and they seem to be on back order and no one is even taking orders for them. so my question is by going from 2.5 turns (suggested in all the manuals as a starting position) down to 1 turn am I still running rich?
    xj650plugs.jpg

    These were brand new before running t around the block 1 time (1/2 mile?) I've tried everything I can think of with no luck.

    Regards,
    Jeff
     
  2. maxim400

    maxim400 Member

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    you might be running too rich, try turning air/fuel mixture screws out a 1/4 turn and start bike, do this until it smooths out , hopefully tis helps.
     
  3. tabaka45

    tabaka45 Well-Known Member

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    On the Hitachi carbs on my XJ700 closing the pilot screws leans the carbs. My understanding is that on some carbs it's just the opposite. My pilot screws are on the engine side of the carbs. Seems that I have read that if they are on the intake side closing them enriches the mixture. Someone that knows your engine and carbs will probably respond pretty soon.
     
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  4. Minimutly

    Minimutly Well-Known Member

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    "I've tried everything I can think of" isn't telling us a lot - what exactly have you tried?
    Float levels would be my first check. Most bikes like to run slightly further out than 2.5 turns, maybe 2.7, so something is amiss.
    Tell us what you've tried?
     
  5. Jeff Witt

    Jeff Witt New Member

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    You are correct "Tried everything I could think of" is a completely useless statement.

    So I started out by shimming the valves, the bike has 27K miles on it so they were a little tight. I had to get a couple of new shims and juggled the others around to get them in tolerance. I rebuilt the carbs. Dry set the float levels to 17.5 MM. wet set the level to 3 MM below the top of the bowl. I cleaned all the gum out by boiling it in lemon juice Then using carb cleaner through all the internal passages. I replaced the V-seals with X-rings from McMaster Carr. I polished the slides down to 1200 grit so they run very free. the diaphragms have no holes compressed air through the chamber sucks them open very quickly. I cleaned all the jets using a welding torch tip cleaner. I was not able to get a small enough cleaner for the Idle jets, Size 40, so I just used a very thin wire (telephone patch wire). I can see light through the pilot jets. I replaced the float valve, cleaned out the idle screw and replaced the tiny O-ring and spring. On assembly I replaced the fuel rail O-rings and set the initial synchronization by shining light through the throttle body using carb 3 as the reference carb and adjusting 4 then 2 then 1 to match #3. I put the carbs back on the bike reconnected the airbox replaced the air filter.

    When the plugs are clean it starts on the first tap of the starter. While it was idling (badly) I sprayed carb cleaner all around the outside of the intakes and around the butterfly shafts absolutely no change in idle speed. Set with the idle mixture screws at 2.5 turns out and it was blowing smoke now they are 1 full turn out and it runs better but still seems like its too rich. I also replaced the plugs with Champion N7YC since they are compatible replacements for the the NGK BP7ES which has been replaced with a resistor plug now. Ordered a good vacuum gauge and a CO2 distribution manifold to build a carb sync tool. I also made a YICS blanking tool so I can vacuum sync the carbs but I do not think the carbs can be that far out of sync to cause this much of an issue. Like I said before as soon as it gets into the needles for acceleration it runs very nice and pulls hard. The other issue it might be is the bike does have a hole in the left muffler just past the collector so the back pressure might be low on that side. I want to get it running good before sinking a bunch more money into an exhaust system.

    Has anyone had an issue with still running rich and the fuel mixture set this low? Everything I have read is that you might need to turn the screws out a bit more as Minimutly suggested, but it's already making my eyes water.

    Jeff
     
  6. tabaka45

    tabaka45 Well-Known Member

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    Sounds like you did a very complete carb cleaning. From my limited experience, your problem is still in the pilot system or with your air filter. When I bought my bike it had a foam UNI Filter and I was never able to get the carbs right until I replaced it with an OEM paper filter I got form Chacal. I would also check the idle jets because the previous owner may have drilled the jets to compensate for a partially clogged pilot system. Can't imaging the plugs causing the problem but I wasn't aware that the Champion N7YC was a replacement plug. If so, it's good to know. But whatever is going on it is the same for all carbs and that's why I suggest looking at the filter and jet sizes.
     
  7. Jeff Witt

    Jeff Witt New Member

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    Actually I am the previous owner. I bought the bike in 1983 with 2300 miles on it while I was in the Army. After I got out, graduated college, got married and had children I parked it in my dad's shed. It's been there since 1992 I got it out this spring as a project bike for my 19 year old son and me to get it running. Now that its fall I need to get it out of the garage so the wife can park her car in it again :) BTW I do have the replacement paper air filter.

    I also cleaned out the fuel enrichment system. All I can think of is that it is getting fuel from somewhere other than the pilot screws. Maybe I should close them completely and see if I can get the bike to start. If it does then I'll know its getting fuel from somewhere else.

    Jeff
     
  8. Rooster53

    Rooster53 Well-Known Member Premium Member

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    If you removed the air jets for cleaning check the installation - the FSM is wrong. If the Pilot and Main air jets are swapped it will cause a rich condition.

    Correct jet placement courtesy of Rick0Matic

    upload_2021-10-11_12-16-38.jpeg
     
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  9. Jeff Witt

    Jeff Witt New Member

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    Thanks for the suggestion Rooster53. I'll have to remove the carbs again to check that. I'm 95% sure that I did put them back in the correct order I have a Haines manual so if its wrong in there then I might have it wrong. One thing I did notice when pulling the carbs apart, mine do not have a plate covering the airjets. While I have them off the bike is ther anything else I should verify before putting them back on again?

    Jeff
     
  10. tabaka45

    tabaka45 Well-Known Member

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    The cover plate is not required. I think I saw somewhere that they actually stopped putting it in new carbs. Also, the Haines manual does have a few things wrong, so Rooster's suggestion is a good one. Hope it's as simple as that. By the way, are the plunger needles on the slides adjustable? If they were removed then maybe they need adjustment.
     
  11. Jeff Witt

    Jeff Witt New Member

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    I think Rooster53 may have something here.

    The Haines Manual shows the Main jet (050)on top and the Pilot jet (205) below it. I think we can say with confidence that the Manual is wrong (RTFM does not apply!)
    haines_jets.jpg Haines-Spec.jpg

    Here is a picture of mine. I was able to remove the hat from #1 without pulling the carbs just to check.
    jets.jpg
     
  12. Jeff Witt

    Jeff Witt New Member

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    Rooster53 that was it. The manual was wrong. I was able to swap the air jets without removing the carbs just pulled the tank and a little careful work with a screwdriver and it runs awesome now. Its idling too high 3k but I think I can work on that.
     
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  13. Jeff Witt

    Jeff Witt New Member

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    Ok the idle was high because the adjustment for the cold start fuel enrichment was holding it open when the lever was fully closed. Made quick work of that and now it hums like a sewing machine. Now to remove the rounded off 12 MM oil filter bolt assembly. I have a 17 MM nut that I'm going to just weld to the bolt head.

    I have to say I really like the engineering on these things but the steel they used is like butter. Japan must have been trying to save carbon back in the 80's. I also replaced every JIS screw that I removed with some steel hex head screws. That makes any kind of work around these bikes so much easier. I would advise it if you are rebuilding anything on one of these.
     
  14. Minimutly

    Minimutly Well-Known Member

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    Result then - nice..
     
  15. BENJAMIN THORNE

    BENJAMIN THORNE New Member

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    I wanna jump in here and thank all of you. I recently bought this bike (82 xj750 maxim) in a state of neglect. I had been at my wits end with these carbs, having them on and off more times than I can remember, checking all of the aforementioned steps to fine tuning and still absolute fouling the hell out of two sets of plugs. At the point of almost breaking, I found this post with the solution(and without having to take the carbs off!!) Thank you so much. Finally moving forward.
     
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