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  1. #1

    Join Date
    Dec 2012
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    Corpus Christi, Texas
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    Lightbulb Lean Runaway Condition After Carb Rebuild

    First time post here: I have a 1997 Yamaha Wave Venture 760 with twin carbs (Mikuni 44ís). The ski is mostly stock, but does have a fuel primer and removed choke plates. The ski had been running fine, except for a little hesitation when adding some throttle on the water. I decided to take it to a local PWC repair shop for a carb rebuild and a new throttle cable. I also had them block-off the oil pump and convert to pre-mix.

    I got a call from the shop several weeks later. They told me that they replaced the throttle cable and blocked-off the oil pump, but that I needed 2 new carbs. They said that they had rebuilt the carbs over and over, replaced all the carb parts, but couldnít get the ski to idle anymore. They told me that there are some internal carb ports that are not accessible and that these must be clogged.

    This didnít make any sense to me, as the ski had been running before I took it to them for the carb rebuild. I picked-up the ski, took it home and started it in my driveway on the hose. The ski idled normally for about 1 minute, then it idled up and down at random for about 5 seconds and preceded to runaway WOT (diesel). This lean runaway is definitely by-passing the entire ignition system including spark plugs. The only way to shut her down is by priming the heck out of it with open throttle or restricting the air intakes.

    My first thought was that I have an air leak somewhere. I tore the ski apart and did a leak down test on the engine block by plugging the exhaust and intake ports. I pumped 10psi of pressure into the block. It only had a 3psi loss of pressure in a 24 hour period. I pressure tested the fuel level sensor, cleaned fuel tank, replaced the fuel/oil premix, replaced all fuel lines, replaced pulse lines and double checked the intake gaskets under the carbs. I double-checked everything on the fuel delivery side, except for the carbs. The ski is still experiencing a lean runaway condition after about 1-2 minutes of normal idle. So now Iím back to the carbs as being the problem. I have 2 questions.

    1. Could the PWC repair shop be correct? Are there inaccessible carb ports that could be clogged and the carbs are just not repairable?

    2. If there is a possibility that the carbs are repairable? Where should I start first when rebuilding? What areas of the carb would cause this type of lean runaway condition? Pop-off, metering valves, etc.?

    Any ideas? Thanks!


  2. #2
    mudslanger's Avatar
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    Jul 2010
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    You should remove the carbs. and totally disassemble them check everything and submerge them in a good carb. cleaner.
    Post some pics of the carbs.
    you may need new carb. kits if the shop didn't install new mikuni kits also put new needle seats in them if the shop didn't.
    if they did replace the needle seat then what size.

  3. #3

    Join Date
    Dec 2012
    Location
    Corpus Christi, Texas
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    Thanks. I'll disassemble them and post some pics. The invoice from the shop rebuild shows "WSM SeaDoo Carb Kit"??

  4. #4
    Predator-x's Avatar
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    Probably the SeaDoo kit they used can be used on some Yamaha carb types, make sure they used the right kit for the job.
    The shop had let you know that some parts where clogged before they proceed with the rebuild, charging you for a half rebuild is not the way to go.

  5. #5
    Myself's Avatar
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    Sounds like they got the return and supply lines backwards. Or a poorly adjusted throttle cable and/or mixture settings.

  6. #6

    Join Date
    Aug 2011
    Location
    san juan capistrano ca.
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    i would rebuild the carbs and use mikuni carb kits ,before you get new carbs, maybe the mixture adjustments are wrong.

  7. #7
    Quote Originally Posted by Myself View Post
    Sounds like they got the return and supply lines backwards. Or a poorly adjusted throttle cable and/or mixture settings.
    +1 this happened to me. Throttle cable

  8. #8

    Join Date
    Jun 2010
    Location
    LKN, NC
    Posts
    22
    clean carbs and blow air through ports and jets. Only use mikuni carb kits.

  9. #9

    Join Date
    Mar 2008
    Location
    Dallas, TX
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    Run it again until it runs away. Pull the ignition tether then open the throttle wide to kill it. Check the spark plugs and see which one or ones were running lean. Make sure the carb and manifold gaskets are good and torque properly. Number 2 carb is usually the culprit due to a bend in the intake manifold. Torque it down to 16 lbs first.
    Last edited by x29c; 02-16-2013 at 04:11 AM.

  10. #10

    Join Date
    Dec 2012
    Location
    Corpus Christi, Texas
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    So check this outÖ I started running through all the suggestions listed above. I really appreciate all the help by the way! I re-checked both gaskets between the carbs and manifold, throttle cable tension, fuel line connections and carb mixtures. All this seems OK.

    I did find out that the rear cylinder spark plug is white after the ski runs away. The front cylinder spark plug is brown. So - I think this means Iím looking at the rear cylinder as the runaway? Is this correct?

    Then I started down the path of disassembling both carbs to submerge them in carb cleaner and replace all the parts with genuine Mikuni carb kits. I took the rear carb apart and here is what I foundÖ The needle seat retaining screw and the low speed jet screw (I think it's a low speed jet?) are completely stripped out. Most of the gaskets are old and brittle, so I donít think the guys that recently rebuilt my carbs replaced any of them. They must have stripped out the screws during the rebuild process, just reassembled the carbs with all the old parts and called me to come pick it up? Iím going to take a stab at removing these stripped out screws, but I may be looking at a new carb if I canít get them out. Iím still hoping to be able to rebuild these. Other than these (2) minor disasters - Does anyone see any other issues with these carb pics? Thanks again for all the help!
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