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Thread: 951 low rpm's

  1. #1

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    951 low rpm's

    I need some input. I have a new to me 99 xp Limited 951. I have changed the grey hoses, fuel valve, new plugs br8es. I have cleaned the carbs, cleaned the tiny internal filters. I have checked all other lines for blockage, taken rave valves apart and cleaned. Checked spark on both cyl. Ski starts right up. It will not go over 4500 rpm. Do you have any direction I can go next? Will the rave on the exhuast cause me a problem? Have not got into it yet. Does a ski this old need a external fuel pump? Thanks


  2. #2
    No external pump necessary. You should check the raves to ensure they are opening up all the way and free of gum. There is a solenoid that controls when they open. For a trial, you can remove the top black cap and run the ski, if it revs up, thats a problem. If not, time to keep looking. If you try this the ski will not have the best bottom end power since the raves can open right up.

    When you cleaned the carbs did you adjust the low speed and high speed adjuster screws? If so they should be set at 1.5 lows and highs closed. This is if the ski is stock.

    When your checking this is it in the water or out of?

  3. #3
    Petron's Avatar
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    what does she idle at? in & out of the water?

    also, is your throttle linkage setup properly?

  4. #4
    KrunchovXPL-GTX-RX's Avatar
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    A 951 will turn upwards of 6500 RPM with no RAVE function.

    That said, this does not mean they are working, just that you may have several somethings happening.

    Have you checked your compression?

    The Water Control Valve (the thing on the muffler that says RAVE, even though it is not) could cost you some RPM if it did not shut off when it is supposed to. That along with the RAVEs being off-line could add up to what you are getting.

    As Petron said, varify the throttle cable adjustment (you should have a little slack in the cable at the carb, otherwise you will be pulling your carbs open at idle and it will go apecrap when you start it on the trailer).

  5. #5
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    are your carbs needles set to specs? I had something similar and my low speed needles were too rich and it would only let me rev up to 45k

  6. #6
    SURFnTURF's Avatar
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    First thing I would check is the fuel selector valve (ON/OFF/RES) did you pull it when you replaced the fuel lines ??If not they usually clog up with gunk and stop fuel flow, this stuff may have already found its way back into the carby internal filter screens even though you cleaned them before.EDIT I just re-read your post, you actually did change over the fuel valve .

    The water control valve doesn't shut water off fully at all at any engine revs it simply reduces water entering the mid pipe at higher revs while still cooling the rubber exhaust couplers.This wont keep revs down below 4500.
    The raves are controlled by the mpem and start to open at 3700rpm to verify that they are not the problem remove the springs under the black caps and test under load on the water ,any change in revs?
    Disconnect the battery and Pull all the mpem AMP connectors and then reconnect being careful not to break the side locking tabs,check that no corrosion is present on wiring pins .

    You will need to verify that it is actually firing on both cylinders ,does it feel real doughy when under load? run it on the lake or on the trailer in the water for a few minutes and pull the spark plugs and see if one is either wet or oily from fuel not being burnt.Proper spark plug colour is a nice chocolate brown on the white ceramic insulator tip.Test and post results.

    The 99s came with a TPS (THROTTLE POSITION SENSOR) When a TPS switch is out of calibration, the ski my run fine for awhile, then all of a sudden drop alot of rpm and run much slower, then it can pickup and run good again, then bad again.
    What is happening is the MPEM is getting the wrong signal from the TPS, sending the timing curve into a retarded mode.It may be your problem as well.??

    The test for a TPS.
    First the TPS when working properly, sends out 5 volts vdc between zero throttle and 80 % throttle, after 80% throttle, it sends zero vdc to the mpem.
    If you see 5 vdc at full throttle, you need to adjust the TPS by loosening the jamb nut on the throttle cable adjuster ( there is a TPS adjuster usually right under the glove box insert. It is inline in the throttle cable). Adjust the adjuster until you get zero volts after 80% throttle.

    To test it you need to connect the voltage meter leads to the wires coming off the TPS ( located under the oil tank on XPL's) Connect the voltmeter between the black/white and a ground. Do not unplug the TPS harness, slip the test lead in along the wire to the switch ( a paper clip works good here) . Depress the stop switch once to power up the ignition system. It will stay on for 30 seconds. Then pull the throttle lever to around 80%, the voltmeter should read zero after 80% throttle. If it does not show zero voltage after 80%, adjust it. If you cannot adjust it to get zero voltage after 80%, replace the throttle cable.

  7. #7
    KrunchovXPL-GTX-RX's Avatar
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    The WCV does not actually shut off the water. After a long assed day at work and half and hour to midnight even I can fail to split the old hair every once in a while.

    A significant enough water leak into the pipe (and full flow at the MPS at higher RPM just might qualify) will knock off as much as 1000 RPM. A blown flange gasket certainly will, I can testify to that one. Add to that no RAVE function and that was what I was thinking.

    Note: I have an LED hooked in-line on my XPL that lights up when the MPEM turns on the RAVE solonoid. As a general rule it does not come on before 6000-6200 RPM unless you pin the throttle off idle (and of course, when you do that who the hell knows what RPM it comes on at since it runs through them all pretty dang fast if I say so myself).

  8. #8

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    Thanks for the Ideas. I did adjust the carbs adjustment screws to 1.5 and 0. I will check the tps adjustment tonight. I have not looked at the plugs since the last time I put in the water to see if I had made any headway on problem. But I do have spark on both plug wires. Will pull plugs and check .
    Ski idles on hose at about 3000 and in water at about 1500. From what I have read on here this is about right. Throttle cable seems to be adjusted correct with a small amount of slack. I would not say it is doughy because it comes up to 4500 rpm's pretty good, then stops but its just not right. As far as I can tell the ski is all stock execot the air filter. Also did not mention it is running on premix, and yes I drained the tank and put new gas and Amsoil oil in it. Same old story the PO said the ski ran fine last year but who knows. Thanks Again

  9. #9
    SURFnTURF's Avatar
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    As posted before do a compression check to verify they are blowing the same numbers . Sometimes spark plugs just stop working at higher revs (especially NGKs for some reason) they do not like firing if their has been water in the bores and will eventually fail.So maybe change plugs as well.

    Is the pisser flowing a constant stream of water or is it spitting or the flow being interrupted when you run it on the lake (not on the trailer) ?

    Try those things first and post back.

  10. #10
    Surf thats a good point about the plugs. When we raced snowmobiles we had a plug that would spark when you ground it to the head, under load the compression would blow out the spark and stop it. New plugs, all set.

    Not saying thats the problem here but a possibility. Especially if the plugs have ever been dropped, they can crack inside.

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