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81 XJ550 Seca starting trouble

Discussion in 'XJ Technical Chat' started by Random, Jul 31, 2018.

  1. Random

    Random New Member

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    hey everyone,

    So a little back story for me, I’m new to Japanese bikes and have limited knowledge. I’ve rebuilt and customized several Harley’s but this is my first serious dive into these bikes.

    I’ve been working on an 81 XJ550 Seca for a few weeks now and can’t figure out the problem as to why it won’t start. It sat for a year before I bought it. Drained the tank, cleaned the carbs, replaced the dry rotted carb boots, new air filter and switched to blade style fuses but I’m not getting anything.

    It’s making a god awful noise whenever I try to start it (see YouTube link). Whenever I take the air cleaner off and spray a quick little spurt of starter fluid into the carbs it’ll start up and run about 4000rpm then lower to 3000. Throttle responds great even though it’s idling too high but after a minute or so it sputters out and dies. I’ve cleaned the every living crap out of the carbs so I don’t know how it isn’t getting fuel. Would a stage 1 help this? Obviously it would need some tuning after the fact if that was the case.

    Also PO had the mixture screws backed out about 4 1/2 turns which I changed to about 3 per the clymer manual.

    Any help would be insanely appreciated because I’m at a loss on this one. Here’s the link to the terrible sound the bike makes when I try getting it going.

     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    is 3k rpm with choke lever on?
    you may need to use it if you are not using it.
    how did you clean carbs?
     
  3. Random

    Random New Member

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    With choke pulled out it’s revving around 5000 so when I push it back it’ll idle around 4000 then slow down after a little bit longer.

    I completely stripped them down and soaked everything that wasn’t neoprene in cleaner. Afterwards I took a small set of carb brushes and made sure everything was clear. Only thing I wasn’t 100% on was the piece with the little filter looking thing on it. I’ve cleaned a ton of carbs but never the Mikuni so it’s possible I missed something important.
     
  4. XJ550H

    XJ550H Well-Known Member Premium Member

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    did you break down the rack?

    use less starter fluid.
    did you clean the enrichment circuit in the carb bowl? the hole where the brass tube goes? and the hole in the bottom of the bowl?
    you should be able to spray cleaner through well and come out hole at bottom.

    vacuum line hooked up to petcock and motor?
     
  5. Random

    Random New Member

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    No I didn’t take the rack down at all, minus removing the plate and the idle screw so I could access the bowls. I’m not used to multi carb bikes so I didn’t want to risk breaking them down entirely.

    I want to say I did clean the enrichment circuit if I’m thinking about the right thing but I may have to take them off the bike and check again.

    When I bought it the vacuum line was attached to the petcock and the “inside carb on the left side of the bike”. Sorry I know they’re numbered but can’t remember which is which. So I’ve kept it that way. Should it be attached somewhere else? The rest of the carb boots just have plugs on them.
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    any port in the intake manifold works . set the petcock to prime for 5 seconds make sure bowls are filling


    cylinders are 1 through 4 starting on left side of bike when you sit on the bike
     
  7. Chitwood

    Chitwood Well-Known Member

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    Did you soak the entire rack? If so the throttle shaft seals are likely toast and while it may not be your only problem, it definitely is part of it.
     
  8. a100man

    a100man Well-Known Member

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    Generally speaking you will have to have the carbs on/off a few times before you have identified all the cleaning 'issues'.. once you have she'll purr like a kitten. For example did you check idle jet flow through those three little holes by the butterfly??
     
  9. a100man

    a100man Well-Known Member

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    Also unless you know history you must check your valve clearances - which is fun..
     

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