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  1. #1
    PWCToday Regular
    Join Date
    Jun 2005
    Location
    Beaver Lake, NE
    Age
    49
    Posts
    100

    1998 XL 760 stumbles at WOT

    My 98 XL 760 stumbles or cuts in and out at WOT. I can watch the tach bounce up and down 2 hundred or so RPMs. From idle to 1/2 throttle it runs perfect. I have replaced the plugs and I am running sea foam in the tank as the previous owner only rode it once in the past 2 years.
    What should I start investigating?

    As always your help and comments are appreciated!

    Hec
    95 Wave Raider 1100
    With:
    GP 1200 five deg nozzle
    R&D Intake grate (Looks like stock with 2 bars cut out)
    R&D Ride Plate (Short one) Flush with the back of the hull.
    Solas YD-SC-I (13-19) Impeller
    Jet Trim Splash Guard

    Carbs have 1.2 N&S, 80 Gram spring #1 & #2, 95 gram spring #3
    Mikuni BN44/164 valve body assemblies installed.
    Fuel pump covers return orifices drilled and 95 jet installed in last nipple out to tank.

  2. #2
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
    Join Date
    Dec 2003
    Location
    Sunny Fla
    Posts
    25,827

    Re: 1998 XL 760 stumbles at WOT

    You need to rebuild the carbs.

  3. #3
    PWCToday Regular
    Join Date
    Jun 2005
    Location
    Beaver Lake, NE
    Age
    49
    Posts
    100

    Re: 1998 XL 760 stumbles at WOT

    Quote Originally Posted by Grumpy Old Guy View Post
    You need to rebuild the carbs.
    Yeah thatís was I afraid of. Does anyone have the pop off pressure, high speed and low speed needle settings specs? Should I order the Mikuni kits or the rebuild kit listed by Yamaha part number 64X-W0093-00-00. It has additional parts like carb base gaskets etc.. Itís double the price of the Mikuni kits.

    Here is a pic of the Yamaha kit



    Hec
    Attached Images Attached Images
    95 Wave Raider 1100
    With:
    GP 1200 five deg nozzle
    R&D Intake grate (Looks like stock with 2 bars cut out)
    R&D Ride Plate (Short one) Flush with the back of the hull.
    Solas YD-SC-I (13-19) Impeller
    Jet Trim Splash Guard

    Carbs have 1.2 N&S, 80 Gram spring #1 & #2, 95 gram spring #3
    Mikuni BN44/164 valve body assemblies installed.
    Fuel pump covers return orifices drilled and 95 jet installed in last nipple out to tank.

  4. #4
    PWCToday Regular
    Join Date
    Jun 2005
    Location
    Beaver Lake, NE
    Age
    49
    Posts
    100

    Re: 1998 XL 760 stumbles at WOT

    More diagnostic info for you.

    Yesterday I took the XL760 out for a few rides. It will only tach out at about 5,300 RPM. It will bounce up and down about 200 RPM's. When the engine starts cutting out, it will cut out at a frequency of about once every 3 seconds. I noticed the engine stumbles pretty much all through out the throttle range. It's much more noticeable at higher RPMS. The lake was like glass so I'm ruling out pump cavitation. I spoke to the previous owner and asked him how old the fuel was in the tank as I received it with a full tank. He said 1/2 of the tank was from last season and 1/2 the tank was from this summer. I have burned through half of what he had in the tank already and have topped the tank off with fresh Non-oxygenated fuel with some sea foam in it, about 6 Gallons. The plugs aren't fouled and are dark brown color. The engine starts right up with a bump of the starter button when cold too. I will check the actual carb settings this week before I take it out for the season just to rule out carb miss adjustment.

    According to SBT
    Low speed setting is 1-5/8" +/- 1/4

    High speed setting is 3/8 +/- 1/4
    95 Wave Raider 1100
    With:
    GP 1200 five deg nozzle
    R&D Intake grate (Looks like stock with 2 bars cut out)
    R&D Ride Plate (Short one) Flush with the back of the hull.
    Solas YD-SC-I (13-19) Impeller
    Jet Trim Splash Guard

    Carbs have 1.2 N&S, 80 Gram spring #1 & #2, 95 gram spring #3
    Mikuni BN44/164 valve body assemblies installed.
    Fuel pump covers return orifices drilled and 95 jet installed in last nipple out to tank.

  5. #5
    PWCToday Regular Baja 252's Avatar
    Join Date
    Apr 2011
    Location
    Kansas City
    Posts
    126

    Re: 1998 XL 760 stumbles at WOT

    It's probably the carbs, but I would replace the fuel filter and check the on/off/reserve switch for a blockage. If the fuel is bad, diluting it won't really help you need to remove it from the tank and get fresh fuel. Also the fuel pick up screens in the tank could be plugged up.
    16 XFS
    11 FZS
    08 SuperJet
    08 SXR 1100

  6. #6
    PWCToday Regular
    Join Date
    Jun 2005
    Location
    Beaver Lake, NE
    Age
    49
    Posts
    100

    Re: 1998 XL 760 stumbles at WOT

    Quote Originally Posted by Baja 252 View Post
    It's probably the carbs, but I would replace the fuel filter and check the on/off/reserve switch for a blockage. If the fuel is bad, diluting it won't really help you need to remove it from the tank and get fresh fuel. Also the fuel pick up screens in the tank could be plugged up.
    Thanks for the tips! I will dig into the fuel filter and fuel pick up screens this weekend. I will also check the fuel on/off/reserve valve. I did switch the valve from on to reserve while riding to see if the stumble would go away. It didn't.

    Hec
    95 Wave Raider 1100
    With:
    GP 1200 five deg nozzle
    R&D Intake grate (Looks like stock with 2 bars cut out)
    R&D Ride Plate (Short one) Flush with the back of the hull.
    Solas YD-SC-I (13-19) Impeller
    Jet Trim Splash Guard

    Carbs have 1.2 N&S, 80 Gram spring #1 & #2, 95 gram spring #3
    Mikuni BN44/164 valve body assemblies installed.
    Fuel pump covers return orifices drilled and 95 jet installed in last nipple out to tank.

  7. #7
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
    Join Date
    Dec 2003
    Location
    Sunny Fla
    Posts
    25,827

    Re: 1998 XL 760 stumbles at WOT

    Cus your carbs need to be rebuilt....

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