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Carburetor help

Discussion in 'XJ Technical Chat' started by Zoot_Suit, Jun 11, 2025.

  1. hogfiddles

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

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    I have yet to come across a rack that can’t be rebuilt…..and I’ll tell you right now, one of the first things I’d do would be to straighten 0ut those throttle shafts as soon as I’d pull them out.
     
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  2. hogfiddles

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

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    Brhatweed…. Your inbox is full
     
  3. Zoot_Suit

    Zoot_Suit Active Member

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    Over four plus decades of turning wrenches, I've encountered MANY things that can 'technically' be rebuilt, but they NEVER work right, EVER. Regardless of me rebuilding them or having professional shops rebuilding the parts. NEW always works. On a good day, rebuilt may get you home where you can replace it with brand new.

    Starters, alternators, carbs, etc... all the same. New is the only way to go.

    Sometimes, things just simply reach the end of their serviceability life.

    I've emailed Hitachi, and I'm sure it'll go nowhere, but it's worth a shot.
     
  4. hogfiddles

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

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    And over 20 years of rebuilding Xj carburetor racks, I haven’t had one that wasn’t successful.

    so we have different experiences and opinions.

    I have nothing more to add.
     
  5. Minimutly

    Minimutly Well-Known Member

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    I'm sorry, but you are wrong my friend. New is only a collection of working parts, if all parts are good, assembled correctly, a rebuild will work. On carbs the wearing parts are the throttle shafts and spindle bores, the emulsion tube tops, pretty much that's it. Luckily the Hitachi carbs don't suffer much in the throttle wear department...
    So if they are inspected, parts replaced as required, floats set correctly, wet set checked, and synched, all will be well.
    Good luck with Hitachi
     
  6. Zoot_Suit

    Zoot_Suit Active Member

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    ...and used parts, are not new parts, therefore I am correct. Old, tired, worn-out parts, have to be replaced.

    A carburetor is more than just needles, jets, and shafts. The carb body could be worn where those components rest, they could be warped, have micro cracks, etc... all stuff the naked eye would never see. Hence, replacement is best. Of EVERY component.
     
  7. Zoot_Suit

    Zoot_Suit Active Member

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    I have 3 friends, who between them, own over 50 motorcycles, and each has 30-40 years experience of wrenching on motorcycles, one of those friends is a certified mechanic. Last week, he came over and watched me rebuild them, while he read the manual out loud. He came to the same conclusion as I did. The carbs are shot (yes, a rarity, but not an impossibility). He told me yesterday that I was wasting my time bothering with them anymore. However, as there are no BRAND NEW carburetors available, and despite my justified bitching, I am also hopeful, and nearly relentless. I honestly came to this conclusion last year. But I've decided to keep trying.

    The weird thing is, for most of the riding season last year, these carbs fought me tooth and nail, then about 2 weeks before the riding season was over, the bike ran perfect. This spring, the carbs again fought me tooth and nail, then started working perfectly for 2 weeks, and without changing a single thing, they started running like crap again.
     
  8. Roast644

    Roast644 Well-Known Member

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  9. Brhatweed

    Brhatweed Well-Known Member

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    Dunno man... I'm not a "professional" just experienced. I've been tinkering with bikes & engines since I was a little kid in the 1970s. First was a little purple Rupp Roadster and later the RMT-80 before moving to a Kaw KDX-175, Honda 250 scrambler and eventually a 1980 CBX sport and now a SECA 750. My first "chopper" or custon was a Chaparral that I stuffed a 12HP Briggs engine into at 14. Golden horseshoe up my... could be. What I have learned over the years is to take it slow and don't cut corners be it with a little Kehin or Quadrajet. If it worked before it can work again unless it's been altered to the point of destruction. Hitachi HSC32? a vacuum balancing act. Could they be shot? Maybe but this is also more opinion based than factual esp when those working on them don't have a clear understanding.

    You want another honest opinion by a someone with HSC32 experience I'm available, I'm not looking to make a buck here as this is one bike guy helping another. Up to you.
     
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  10. Zoot_Suit

    Zoot_Suit Active Member

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    I was able to source a fuel bowl with an operable drain screw. Now I can do the "sight tube" method to set the correct fuel level... I'll just have to move that bowl from one carb to the next.

    I will be breaking the rack, and rebuilding them from the ground up.

    Snapchat-661460180.jpg
     
  11. Zoot_Suit

    Zoot_Suit Active Member

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    Son of a gun!

    Snapchat-850304405.jpg
     
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  12. Brhatweed

    Brhatweed Well-Known Member

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    Very possible but do keep in mind the rubber gaskets swell and shrink over time in the presence of gasoline while the paper ones often stick. I hand cut my own gaskets from manilla paper (yellow) folders using a leather punch to make the various holes, reason for this is my rubber gaskets swelled up bad when I ran 100LL AvGas in the bike and began to leak... not a something I wanted with $8.55/gal fuel in the tank. And FYI the fuel added nothing but a distinct smell to the exhaust.
    One can cut their own gaskets using gasket material or going with a thick paper stock like a file folder, as long as the dimensions and locations of the slots/holes are exact they won't cause any problems.
     
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  13. hogfiddles

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

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    Doesn’t look like an original gasket.
     
  14. Zoot_Suit

    Zoot_Suit Active Member

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    The OEM is the factory gasket from 1982, it's just severely compressed and hard as a rock.
     
  15. Zoot_Suit

    Zoot_Suit Active Member

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    The tab on the #3 carburetor that the idle screw presses against was actually cracked and wiggling back and forth, so I cracked it all the way off with my fingers, then fabbed a new piece from higher quality steel and riveted it on.

    I considered welding it back on, but it's such a low grade metal, it would have just melted away (with my 95 amp flux core with .035 wire). I figured riveting it was the safer option. It seems to be holding strong.

    20250708_172920.jpg
     
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  16. Zoot_Suit

    Zoot_Suit Active Member

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    Noooo... I don't need to clean off my workbench...

    Snapchat-2105468736.jpg
     
  17. Zoot_Suit

    Zoot_Suit Active Member

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    Okay, sight tube method done.

    Carb 1:
    Float start: 17.5mm
    Fuel level: -3mm
    No change needed.

    Carb 2:
    Float start: 17.5mm
    Fuel level: -3mm
    No change needed.

    Carb 3:
    Float start: 17.5mm
    Fuel level: +3mm (fuel level was above the bowl) o_O
    Float change: 18mm
    Fuel level: -3mm

    Carb 4: (weird one)
    Float start: 17.5mm
    Fuel level: -4mm
    Float change (3 times, up and down): ended at 19mm
    Fuel level: -3mm

    If it's not storming tomorrow, I'll be able to reinstall the carbs on the bike and see what happens...
     
  18. Minimutly

    Minimutly Well-Known Member

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    Have you sorted out the bent linkages, there is no way in the world they should be as they are, that all the enrichment slides close (and open together), also checked the slide needles are genuine? Assuming all the jets are correct Yamaha ones and in the right place?
     
  19. Zoot_Suit

    Zoot_Suit Active Member

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    Linkages are at 90°, the slide needles are aftermarket as the OEM were corroded due to sitting in a barn for 19 years with fuel in the carbs.
     
  20. Zoot_Suit

    Zoot_Suit Active Member

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    Do you feel the pain? o_O

    9zrx8i.jpg
     
  21. Minimutly

    Minimutly Well-Known Member

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    BIN THE NEEDLES!
    Get some new ones from @chacal , pretty much everything on eBay for these carbs is junk, jets, needles, manifolds. Did you incrementally measure the old vs new needles? I'd be shocked if they were correct.
     
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  22. Zoot_Suit

    Zoot_Suit Active Member

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    I mic'd them out (the slide needles), they seem to be absolutely identical. That seems to be the ONLY carburetor part that's correct. :D

    The jet needles are about 0.1 mm taller than the OEM, but that was difficult to measure because the OEM needles were absolutely shot.
     
  23. cds1984

    cds1984 Well-Known Member

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    I've wondered about the eBay kit needles. The ones I've seen are brass where the originals were aluminium. You'd think the extra weight would add to the pain of tuning also.
     
  24. Zoot_Suit

    Zoot_Suit Active Member

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    My OEM needles were brass, the aftermarket are aluminum. Weird.
     
  25. hogfiddles

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

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    I absolutely refuse to use eBay kits. I have had a few people send them with a rack to rebuild……”i already bought these, can you use them?” Ihave not had a SINGLE one of them work correctly. Put correct ones in, problems disappear.
     
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  26. cds1984

    cds1984 Well-Known Member

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    Just wondering. Hitachi is aluminium needles and mikuni are brass? I assumed this but now I'm wondering. Thanks!
     
  27. Zoot_Suit

    Zoot_Suit Active Member

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    Who knows what was happening on the assembly line four decades ago? ‍♂️
     
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  28. hogfiddles

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

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    In 20+ yrs of rebuilding racks, I have only ever seen aluminum needles as original. Brass ones have always been aftermarket. Granted, somebody may have come across brass originals, but I personally have not.
     
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  29. Zoot_Suit

    Zoot_Suit Active Member

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    My bike only had two previous owners and neither ever did any maintenance to the bike before it was parked in a barn for 19 years. The bike only had 12K miles on it. And it was all original, including the light bulbs, tires, and oil... o_O
     
  30. Zoot_Suit

    Zoot_Suit Active Member

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    Okay, I got the carbs back on the bike, and did about a 30 mile test run, with about 8 miles of city and 20 miles of highway.

    The idle is soooo much better, much smoother and consistent.

    The only issue I'm having is the RPM'S don't like to drop down unless I blip the choke, then it idles normal again.

    Any ideas?

    Sticking slides?

    ...oh, and the "choke" only causes the bike to die, it doesn't raise the RPM'S.
     
  31. hogfiddles

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

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    Did you do a running sync?
     
  32. Zoot_Suit

    Zoot_Suit Active Member

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    No.

    No blanking tool... that is probably the next step. However, I don't believe that would cause the issue.
     
  33. Simmy

    Simmy Well-Known Member

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    for sure it will.
    You can synch them without the blanking tool.
     
  34. Zoot_Suit

    Zoot_Suit Active Member

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    They've been bench sync'd. And even checked with a vacuum guage (rather pointless without blocking off the ports though).
     
  35. hogfiddles

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

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    1. Bench sync and running sync are two totally different things.

    2. there are differing camps regarding the blanking tool. I’m in the camp of “you don’t HAVE to use it”. I have one… it’s still in the plastic. I NEVER have used it. Never needed to.
     
  36. Zoot_Suit

    Zoot_Suit Active Member

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    Just went for a 56 mile ride. Seems I corrected the high idle by backing of the idle 1/8th of a turn, and it stopped revving back up to 3K RPM'S, It's now idling at 1,400 RPM'S, and not climbing up on its own.

    However, in 56 miles (42 of which were highway), I burned 2.283 gallons of fuel. Giving me only 25.5 MPG. Better than the 15 I was getting, but still not near the 40 or so it should be getting... although, there may have been a dozen or so times that I rapidly climbed to, and exceeded triple digit speeds... allegedly...
     
  37. Huntchuks

    Huntchuks Well-Known Member

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    Shouldn't your idle be set to 1050 - 1100 rpm?
     
  38. Zoot_Suit

    Zoot_Suit Active Member

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    It stalls below 1,300.
     
  39. hogfiddles

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

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    Can you give us a video of it at idle?
     
  40. Fuller56

    Fuller56 Well-Known Member

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    "triple digit speeds"? That fuel mileage sounds about right. If you want to get 40 mpg you need to remain a lot closer to 55 or 60. Remember how much wind drag you have. As an example, my fuel injected '09 DL650 gets 63 mpg at 55 and 38 mpg at 80, and it is a lot cleaner through the air than a naked XJ.
     
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  41. Brhatweed

    Brhatweed Well-Known Member

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    I get between 36 to 40 on my with my 750 seca running about 70 MPH with #124 main jets. At 55-60 it can touch that magic 50 mpg on a level road however I don't ride for the MPG's

    I've also sync'd my carbs many times without the YICS block-off tool, it takes a little more time to finesse things but it can be done. I don't look for the hard numbers or go for the exact, as long they're within an inch of each other and the idle screw turns are within say a quarter turn of each it will run well. I have one of those four gauge clusters with the little valves on the ends of the tubes, I moved them down closer to the carbs and adjust them just enough to keep the needles moving with just a touch of a twitch. Valves near the carbs allows the hoses to act as dampers and this helps a lot. Idle is around 1000-1200 and it's dead smooth but I've also shimmed my valves to the book and this plays a big role in the overall idle quality and carb settings so if they're not set right don't expect the engine to idle well if at all below say 1500 or so.
     
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  42. Zoot_Suit

    Zoot_Suit Active Member

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    Yeah, I have, and used a four gauge set. It says they're all identical... because the ports aren't blocked by a blanking tool. I'll probably do the rag trick for a blanking tool and get a better idea with the gauges. But that'll be in a few weeks. I have a packed schedule for the next week and a half or so.

    I'll be riding down to Sandusky next weekend for a Memorial Run for a Marine I served with who didn't make it home.
     
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  43. Minimutly

    Minimutly Well-Known Member

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    I've never synched a yics engine, but when the experts tell you it can be done without the tool then I would listen up.
    Some things to note, hard acceleration draws a lot of fuel, so if your riding has a lot of pulls from rest to the speed limit, or above, you will not get anywhere close to 40mpg.
    One other thing, did you change the slide springs? You've said you measured the needles and they were identical (although the originals don't sound like originals and I would be getting hold of some to compare at least), but the springs on Hitachi carbs are really weak affairs, any stiffer will really richen up the mixture.
    This, doesn't go away, and I agree wholeheartedly:- (see below message)
     
    Last edited: Saturday at 5:52 AM
  44. Minimutly

    Minimutly Well-Known Member

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  45. Zoot_Suit

    Zoot_Suit Active Member

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    I've seen the community is very split on needing to sync with the tool vs not needing to.

    But as I've said, in a few weeks I'll do it with the rag method. (Stuff a rag in there to block the ports rather than use the tool).

    The city driving absolutely kills MPG, especially driving in a city like Detroit. And yeah, the elevated RPM driving kills it too.

    But, it's a bit of a relief to find the issue was the new parts (primarily the gasket) and to have it running better.
     
  46. Minimutly

    Minimutly Well-Known Member

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    Let's be honest here, synching will massively improve the idle setting consistency, provided the carbs are mechanically consistent, is all working correctly in the linkages. However, it's not going to make a massive difference to your fuel consumption, so if under steady riding you are still in the 20s you have jetting issues...
     
  47. Zoot_Suit

    Zoot_Suit Active Member

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    It's the factory jets.

    It's idling much better now that the floats aren't getting intermittently stuck on the gaskets.

    I suspect a significant reason the MPG is down there in the mid 20's is the loose nut between the seat and handlebars. :cool:

    I'm going to go for another ride today and I'm going to keep the RPM'S and acceleration within reason and see how it does.
     
  48. Zoot_Suit

    Zoot_Suit Active Member

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    Just got back from another test run, this time keeping the RPM'S and speed in check.

    55.5 miles and 1.706 gallons of fuel.
    Giving me 32.5 mpg. Much better than when I'm in the throttle... who woulda thunk it? :D

    I'll edit and upload the video to YouTube sometime tonight or tomorrow.
     
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  49. Brhatweed

    Brhatweed Well-Known Member

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    Those are numbers I can live with but again I don't ride my SECA for the MPG's.
     
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  50. hogfiddles

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

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    Or the needles/emulsion tubes are worn……or a combination of those AND jets…..
     

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