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750 and 650 carbs the same?

Discussion in 'XJ Technical Chat' started by On1wheel01, Jun 15, 2007.

  1. On1wheel01

    On1wheel01 Member

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    Ok I'm tryin to figure out if the carbs off a seca 750 are the same as a 82 seca 650. They look identical. Because my 650 carbs are in better looking shape.
     
  2. KiwiXJ750D

    KiwiXJ750D Member

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    HSC 32 for both models. The internal jets are different, swap 'em!
     
  3. On1wheel01

    On1wheel01 Member

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    Ok I'm gonna put the stock header(750 It looks larger is it?) with a set of slip on(guttted out) pipes and pod filters, should I re jet?
     
  4. RickCoMatic

    RickCoMatic Well-Known Member

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    The magic word is: Pod Filters.

    Pod filters increase the amount of air introduced to the design element ... exponentially!
    The total amount of Cubic Feet per Minute allowed to be drawn through the rubber Air Inlet on the Airbox and shared among the four carbs after passing through the air filter ... is LESS than what is drawn-into only one Carb with a non-restrictive Pod Filter.

    The engine is forced to be LEAN.

    You'll need a Jet Kit ... or, a Complete Set of Richer Jets, bought ala Carte, to begin the process of (possibly never) finding an ideally Correct Air-Fuel Ratio to have the bike run in a state of "Fine tuning."

    As the testimony of nearly all who make the transition from the Engineered Designed Performance of Stock Exhaust and Centralized Joint Air Intake to Exhaust Headers and Individual Intake Filter Pods ... attests:

    "You'll Need to re-jet ... and, re-jet ... and, re-jet ... and, re-jet ... Until you wish your carbs were fastened on the bike with Velcro."

    If there was a formula that would positively allow you to fine-tune a YAMAHA XJ-Series Engine, manufactured for retail, that has been altered with Performance Exhaust Systems and Intake Pods substituted for the Stock shared Airbox ... that formula would be known and published, here!
     
  5. KiwiXJ750D

    KiwiXJ750D Member

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    Maybe!

    check here: Jetting help

    The way the CV carbs work on the XJ makes it "fun" to try and get things working right with non standard air box and/or pipe. Saying that you might get away with one size up on pilot and rasing the needle position.
     
  6. BlueMaxim

    BlueMaxim Active Member

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    That means the needle jets also. The 650 uses Y-10's and the 750 Y-13's.
     
  7. On1wheel01

    On1wheel01 Member

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    Ok so I should go with Y-14's? And where could I find them at a decent price.
     
  8. kevineleven

    kevineleven Member

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    Not to purposely contradict anyone... But I have pods and a very VERY short&open exhaust, and I haven't re-jetted. My bike runs like a top. Given, I did work the colortune, and vacuum gauges overtime to get it dialed in, but it's there, and absolutely screams with no hesitation, missing or backfiring whatsoever. Maybe my bike is just "different".
     
  9. KiwiXJ750D

    KiwiXJ750D Member

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    It's not contradicting, some just seem to be OK. I used to have a XJ650 midnight with a 4-1 short & open exhaust and it ran fine too. It's just if it doesn't they can be a real PITA to get right. The 650 4-1 did not improve preformance either, was not very impressed.

    You will have more top end with your setup and may find uping the main jets size improves your preformance. What do your plugs tell you?
    The EFI runs lean from the factory and Dave told me the carbed XJs will start running away from the EFI at over 5,000 RPM.
     
  10. RickCoMatic

    RickCoMatic Well-Known Member

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    Don't worry about contradicting me.
    My bike's Stock.

    What do I tell everybody else who thinks the FIRST Cosmetic Mod they are going to make is taking a hacksaw to the airbox and sticking-on a set of Pods?

    I simply don't recommend it.
    In some cases you need to Pop-up a jet size just to be able to run with a K&N Air Filter in the Box.

    Then they start asking:
    How do I re-jet ...
    How do I get the carbs off
    How do I fix the broken Cap Screw I told them NOT to mess with
    And, then i have to be the bearer of the Bad News.

    Unless someone has the experience needed to do the whole job for themself ... I don't recommend it.

    I don't want to feel like I gave somebody directions to the Secret Swimming Hole ...
    and later, find-out they drowned!
     
  11. On1wheel01

    On1wheel01 Member

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    Ok well is the air box on the 750 the same as the 650. We busted the junk yard 750 box. But my 650 is mint.
     
  12. Robert

    Robert Active Member

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    They are slightly different between my 81 650 and 750. Not sure if they will easily swap.
    Side note: you must remove the engine to swap out air boxes. No other way around it without breaking the assembly.
     
  13. On1wheel01

    On1wheel01 Member

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    Ok yea thats how the 750 air box bit the dust, we took it out first. I am still trying to decide between trying to make the 650 box work, or buying pod filters. Hopefully my current engine will last till winter, and I will change them out then. Hey Robert since you have both a 650 and a 750. Is their much power diff in them?
     
  14. Robert

    Robert Active Member

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    A bit of course but that is expected (based upon memory). More CCs = more power. I've not had my Seca road worthy in many years (correcting this issue as we speak) and the Max is waiting for the engine to be installed (two years and counting, also on the plate) so a fair comparison is hard to provide at the moment. Thank goodness the FZR fell into my lap when it did or I would have been wheel-less!
     
  15. RickCoMatic

    RickCoMatic Well-Known Member

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    You must have a great place to be able to store and keep all those projects going.

    I'm down to having to move a bike outside ... or, I can walk-around the one being worked-on.

    But, the family room expansion is over and all the stuff that was piled-up in the shop has been moved back out of here.

    My body work and painting space is GONE. So, total restorations are out of the question.

    You never have enough space no matter what.
     
  16. On1wheel01

    On1wheel01 Member

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    Yea you can never have enough space. I am doing all my work in my one car garage and I would love to have a dbl.
     
  17. Robert

    Robert Active Member

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    Amen brother, never enough space. I rent a 10X20 for $180 a month. It houses 2 of the rest of the fleet. And my rollaways, and my electronics equipment....etc. I at least still have access to my garage (Mommy said I could have one room in the house for my own, no brainer there). Epoxied the floor and installed tunes, I'm ready to roll!
     
  18. RickCoMatic

    RickCoMatic Well-Known Member

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    I gave-up a ton of Shop space to please the Massey women who wanted to lounge on a sectional, watch DVD's in Surround-Sound and play with the kitty-cats on new carpet.

    They let me do "The Sound"

    I'm happy to be able to go-in ... patch-in my drum kit and set the Play mode to Studio.

    It's like being in a recording studio with the band.

    If Nigel Olsen or Liberty D'Vito come-down with Hepatitis and Elton or Billy needs someone to sit-in with the band ... I'm ready!
     

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