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  1. #1
    PWCToday Guru E350's Avatar
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    '88 X2 650cc - RPM Drops at WOT

    I have been riding my wife's 1988 X2 650cc alot recently. It starts immediately, runs like a raging bull, and is hella fun to ski!

    I noticed that the throttle cable was adjusted to what I thought was a little tight (so that it prevented the throttle from opening all the way to rest on the throttle stop). So, I lengthened the carburetor throttle cable. And now when I squeeze the finger throttle it opens all the way to the stop.

    Carb is a Mikuni BN 44 (I believe) with the tall conical K&N flame arrestor.

    Works fine at WOT on the trailer with the hood off or on.

    But on the water when I pull the finger throttle past where the cable used to stop it, the ski drops rpms.

    At first I thought that it was not getting enough air for the additional gas which the carb is/should be introducing.

    But now I wonder if it is the "rev" limiter or something else?

    I need a decision tree to diagnose this condition. Any suggestions?

    Also, BTW I have an induction timing light which has an rpm gauge on it, but it is not waterproof so I don't want to take it on the water. Any good recommendations for a waterproof tachometer to see what my actual rpms are?

    I will post up a picture of the carb tonight. Hopefully you guys and gals can verify the carb make and model.
    Last edited by jerrspud; 09-14-2017 at 06:11 PM.

  2. #2
    Top Dog bandit88's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    At what throttle position was the cable stopping at before? I would be willing to bet that the high speed screw needs adjusting. Also ditch the K&N, when they get wet they choke down the carb.
    -95 750SXI
    -86 440 with PJS800 conversion
    -90 TS650

  3. #3
    PWCToday Guru E350's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    bandit88: The cable originally stopped about an 1/8" above the throttle stop on the carburetor.

    I thought it was only the Ocean Pro square flame arrestors with the fuzz between the screen which choked down the carb when wet. I will post up a picture tonight.

    (You know that would explain why it only does it riding though... Maybe I will take the K&N off the carb for tonight's riding session and see if that makes a difference.)

  4. #4
    Top Dog bandit88's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    Oh, do you have a restrictor in the return line? BN44s Need a restrictor otherwise they loose fuel pressure. I always use a main jet, something like a 140.
    -95 750SXI
    -86 440 with PJS800 conversion
    -90 TS650

  5. #5
    PWCToday Guru E350's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    Hmmm...

    The engine was built by a very good engine builder named Eric Burton, so it likely has the required restrictor. But I will look tonight. So, question:

    Is the restrictor placed in the fuel line going to the carb?

    or

    Is the restrictor placed in the return fuel line leaving the carb heading back to the fuel tank?

    And since the ski sat for gee wiz, I dunno, maybe 15 years, I guess the "restrictor" could be gummed up. So, it would be good for me to find and inspect it.

    This topic probably explains why the engine builder put the primer on its own port from the tank.

    On my '93 550sx, I just put a "T" in the fuel line to the carburetor and ran the primer off the "T". Should I have run a separate line from a port in the tank for the primer in the 550sx? It has the Keihin 38mm I believe.

    Now I am curious and want to see how the primier is set up in the '94 Superjet.
    Last edited by E350; 09-12-2017 at 05:08 PM.

  6. #6
    Top Dog bandit88's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    The restrictor will be in the return line, if it has one. If I can, I always run a primer off its own line, then you dont risk getting air in the main fuel line if the primer seal goes bad. Having it T off the main line is pretty standard though.
    -95 750SXI
    -86 440 with PJS800 conversion
    -90 TS650

  7. #7
    PWCToday Regular IamMikeM's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    If the ski has been running fine up until now, you probably have the restrictor. I would look into getting new crank seals if it has been sitting that long. I use a K&N with no problems with water ingestion. Just make sure it's well oiled and the water wont soak in.
    87 X2 650, Bad Bones head and reeds. Mariner ex manifold, Coffmans stainless steel pipe, Mariner waterbox, Jetinetics flywheel, Dales Bad attitude ign, Westcoast intake, SBN44, K&N flame arrestor, TRD throttle wheel, Bullettproof stem, Renthal bars, KVPI finger throttle, Mariner deep intake grate. Dual cooling. billet coupler set, Scat Trak 8-16, Blueprinted and extrude honed pump. PJS rip turn. 1.5 chop.

  8. #8
    Top Dog bandit88's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    Quote Originally Posted by IamMikeM View Post
    If the ski has been running fine up until now, you probably have the restrictor. I would look into getting new crank seals if it has been sitting that long. I use a K&N with no problems with water ingestion. Just make sure it's well oiled and the water wont soak in.
    He has a K&N airfilter, not a marine style flame arrestor. Also, he said it was running fine, but the cable was preventing the throttle from opening all the way, the issues happen when the throttle is opened more.
    -95 750SXI
    -86 440 with PJS800 conversion
    -90 TS650

  9. #9
    PWCToday Guru E350's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    bandit88 I am pretty sure that it is the K&N marine cone shaped flame arrestor. But I will take pictures. And I hope that it does not have gauze in it.

    IamMikeM: banditt is correct on the symptoms. I am just trying to get a little more top end at WOT from the engine. If I would just shorten the throttle cable to what it was before, I would be stupid and happy.

    Now that I lengthened the throttle cable, I am stupid and unhappy, because I am greedy and want to squeeze all the power out of that raging 650cc engine I can at WOT!!!

    One more thing guys, what is an accurate tachometer I can run to determine whether I am getting anywhere near the rev limiter at WOT?

    Thank you both for your help.
    Last edited by E350; 09-12-2017 at 06:02 PM.

  10. #10
    PWCToday Guru E350's Avatar
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    Re: '88 X2 650cc - Idle Drops at WOT

    This is how far the throttle butterfly opens now that I extended the throttle cable to allow the throttle lever to rest on the carburetor stop at WOT:

    DSC03585- lq.jpg

    This is approximately how far the throttle butterfly opened before I extended the throttle cable (the lever stopped about 1/8" from the throttle stop):

    DSC03594- lq.jpg
    Last edited by E350; 09-13-2017 at 01:21 AM.

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