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1982 Yamaha Seca 650 (Project)

Discussion in 'XJ Technical Chat' started by firebane, Jun 27, 2019.

  1. firebane

    firebane Active Member

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    100% Canadian so I know the jetting is a bit different.
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    Years & Models: 1980-1 XJ650 Maxim, Midnight Maxim, and XJ650RJ and RJC Seca Canadian models
    Carb Manufacturer: Hitachi
    Carb Series: HSC32
    Carb Model ID: 4H800
    Main FUEL Jet Size: #110
    Pilot FUEL Jet Size: #40
    Main AIR Jet Size: #50
    Pilot AIR Jet Size: #195
    AIR COMPENSATOR Jet Size: #36
    Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
    Main jet NEEDLE ID: #Y-12
    Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
    Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
    Idle RPM's: 1,050 rpms
    its running. you may want to install correct air jet
     
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  3. firebane

    firebane Active Member

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    So forgive me as I'm trying to learn what all these jets do... and perhaps the air jet is causing my issue now.

    So last night I moved up the clip to lean out the bike and today I set the screws to 2.5 turns out but it didn't seem right. I then moved them to 3 and it was getting better then I moved them just a bit past 3 of maybe 1/8 turn and the bike no longer stumbles at low rpms and has a SMALL stumble around 6500-7000 and can work through it then rev to 8,000 without issue.

    I'm going to adjust the screws out a bit more to see if I can clear that up and if I can assume then as we are figuring that the pilot jet needs to be lowered.

    Correct in this thinking?
     
  4. XJ550H

    XJ550H Well-Known Member Premium Member

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    pilot air jet is oversized and at 43 so is the pilot jet. you will only want to change 1 thing at a time.
     
    Last edited: Jul 30, 2019
  5. firebane

    firebane Active Member

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    So I'll probably just buy that carb bank to have a spare set on hand and original parts.

    With that said after turning out the screw a bit more and went for a ride I noticed a few things:
    a) Popping on decel
    b) 1/8 to about 1/4 throttle good response
    c) Anything after about 1/4 throttle and cracking the throttle bogs down
    d) The throttle response on this thing now is absolute nuts and just wants to go lol

    I'm thinking I'll drop the needle down and see how it runs from there and order the carbs and get those jets looked at.

    But I'm pretty damn happy with where it is right now compared to where it was.
     
  6. Polock

    Polock Well-Known Member

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    air jets work backwards from fuel jets, bigger air jets run leaner
     
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  7. k-moe

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

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    +1 And you're already running lean. Popping on decel is the clue on that assessment.
    You need the correct main air jet at a minimum.

    And again, dropping the main jet needle leans the mixture, which is the opposite of what you need to be doing. That bog is a lean bog, not a rich bog.
     
  8. Polock

    Polock Well-Known Member

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  9. firebane

    firebane Active Member

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    Good to know and makes sense.

    Yeah, wasn't sure which way to go so I apparently went the wrong way :D I'll drop it down again and adjust from there.

    Tough to know what to do when you feel like your starting from scratch, but now I feel like I have a fairly good baseline :D

    Thanks will look it over.

    Also just ordered those carbs.

    Even through these trials and tribulations and not really being able to ride the bike at all this year... the short jaunt tonight with how it is now running better than last year put a substantial smile on my face.
     
  10. firebane

    firebane Active Member

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    Well decided to drop the needle clip down 1 and well the bike just runs like crap again. Before I did it at least it would go and actually want to go.. but now.. blah.

    So I think I'm done farting around until I get that other set of carbs and start changing out the air and main jets and if need be ... the needles.
     
  11. firebane

    firebane Active Member

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    What do you do when your carbs are so changed and different that you need to start fresh? You find a virgin set of carbs for $100 CAD

    Now I can do some comparisons and checks for things like slide changes, jets and needle.

    Even the drain screws look like they have never been touched :D

    [​IMG]
     
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  12. Polock

    Polock Well-Known Member

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    you might find that turns out to be a :(
     
  13. firebane

    firebane Active Member

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    I have good coaxing skills... good penetration lubricant and some heat and even the most stubborn holes become easy to work with.
     
  14. k-moe

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

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    Matti, don't
    ;)
     
  15. gang3

    gang3 Member

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    Are there any other models of carbs that will work with a 81 xj 650 I just picked up another project and the float bowl drain screws are so stuck i cannot crack them open, P.S. Next time i buy a project i might just test these float bowl drain screws and if they are stuck, Its a great reason not to buy the bike, This is the most difficult and expensive part of these old yami`s is the carbs in my opinion, I guess it could be that im not very good at it, last project i had to redo the carbs 2x the project before that was 2x on the carbs then gave up and paid a guy 400.00 to do them. I Guess you could say not my strong suit.And now facing this all over again breaks my spirit dont know what to do about these drain screws even. and offers of help or advice strongly appreciated.
     
  16. XJ550H

    XJ550H Well-Known Member Premium Member

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    you soak them in pb blaster then put in a vise drill a hole in the screw and use an easy out. I use the square screw extractors no need to buy a second set of carbs just for the bowls.. someone here has extra bowls if you needed them
    .
    soak them heat them chill them and soak them then extract

    i use the square extractors and give them a rap with a hammer to set them

    i put kroil in the drain side and the card bowl hole as well as the screw head

    https://www.amazon.com/CTA-Tools-90...t=&hvlocphy=9002383&hvtargid=pla-434809604614
     
    Last edited: Aug 17, 2019
  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    650 and 750 carbs are the same except for the jets and slide needles

    you could bring the bowls to a machine shop and have them extract the screws

    use T handle not a spanner

     
    Last edited: Aug 17, 2019
  18. gang3

    gang3 Member

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    UpDate : I Ended up taking the carbs apart to have closer look, I Could tell by the smell after taking the first Float Bowl off I was in for some disappointing fun .Yes they were very bad Geez what do they put in our fuel these days that turns into such a foul substance after a few short months. Any way these carbs were way bad. So I Was able to find a set of 4 carbs a few hundred miles north near Seattle and i bought them had them shipped already. And these are clean im much happier now with those stinking dirty carbs behind me. But I realize the battle is far from over, Now i got to get them to work,Actually they look pretty darn good and 80.00 bucks plus 14.00 shipping was not too bad.
     
  19. firebane

    firebane Active Member

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    Well an update to this thread.. I got the jets all changed out and it runs much better now. The bike isn't perfect and still needs some tuning so I think a carb sync will be in short order.

    Feels so good now that it will want to actually rev like it wants although there seems to be a bit of a "gurgle" if you wish at idle and a bit of a stumble from off idle.

    I'm not sure where I am with the mixture screws but I think I'll set them to 3.5 out and see what happens.
     
  20. k-moe

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

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    If everything else is as it should be, you'll run rich at idle.
     

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