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81 Seca 550: Tank-draining fuel leak and some n00b questions

Discussion in 'XJ Technical Chat' started by brickborg, Sep 19, 2019.

  1. brickborg

    brickborg New Member

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    Evening all, long time lurker that finally got the bike I was looking for- an '81 XJ550 Seca. I come from an automotive background, but working on bikes is obviously foreign to me and I'm in need of some help.

    Biggest issue currently is that there is some kind of persistent fuel leak that happens when the motor is off. The bike sat for about a month while I sorted out insurance and got myself legal to ride- in that time it leaked an entire half a tank and it's reserve all over the street. The only notable place I could evidence of leaking from was the small heatshield under the carbs, so I was thinking first thing to do is replace the needles and set the float level correctly in case I'm getting fuel out the intake boots and draining out the airbox.

    One problem with that though- the petcock was in the "On" position the whole time, which to my understanding is supposed to cut fuel flow completely when there's no engine vacuum. If the bowls are overfull, wouldn't it just leak out the intake until the level got down so far it couldn't any more? If the fuel from the tank is cut off and the petcock is working right, how would it keep leaking until the tank was dry? I'm thinking this is probably toast as well.

    So far I have two likely culprits contributing: the petcock and the needles/float level being wrong. Does my thought process seem about right or am I misunderstanding how the petcock is supposed to work?

    Also, what are the best sources for decent parts these days? Lots of suspiciously well priced parts for the Mikuni's and even rebuilt petcocks for like $10 on eBay. Maybe I'm just wary cause anything for my old euro project car that's cheap is total garbage. Are these parts worth being suspicious of or are these pretty well vetted by now?

    Appreciate any advice you might have.
     
  2. Xjrider92117

    Xjrider92117 Active Member

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    Your thought process is correct. Also I'd suggest to change your oil and filter. The gas most likely contaminated your oil.

    For parts my go to guy is in the upper left corner of every page. Xj4ever. He'll get you the correct parts for sure.
     
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    if your petcock has an ON setting it is not an oem petcock and not a vacuum operated petcock.

    your needle valves are leaking
     
  4. brickborg

    brickborg New Member

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    I should have been more clear- it's not labeled ON, it's consistent with the manual thankfully. It's a three position run-prime-reserve petcock, and it had been left in the vertical position.

    I'm going to order up a manual conversion from XJ4ever and then address the leaking needles/incorrect float height at the same time. Kind of a bummer since I wanted to ride it a bit before MN weather stops play for the year, but hey, not the end of the world.

    Appreciate all the input.
     

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