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  1. #1

    loss of full throttle RPM's, down from 7K to about 5K.... is it the carbs???

    2005 ultra 150, 70 hours, carbs never cleaned or rebuilt, ski sat for 2 months straight this summer.

    Put new gas in, started ski-warmed it up, as I drove through 5mph zone, punched it and it takes off and revs to 7K. All is good. Slow down, pass through a bridge (short 5mph zone) punch it again, and hold it for a full throttle run of about 25-35 seconds, all is good.

    Stop, turn ski around, hit it again full throttle and I get up to 7K rpm's again, but after about 20 seconds there I start to loose rpms, gradually falling to 5K, where it stays, despite holding the throttle wide open...

    I back off throttle to idle and float around for a few minutes...Try it again, and it won't rev past 5K... I back off throttle and idle for a few minutes, try again, and up to 7K we go, only for it to gradually loose rpm's and hover around 5K again... I back off, idle around again for a few minutes and the hole shot is real lazy, max RPM's is about 5K again.

    I'm just about on plane and I pop over a boat wake, prop cavitates and revs increase, as the ski lands back down it takes off up to 7K again...

    The are no warning lights on the dash.

    Any ideas what is causing this loss of rpm's?


  2. #2
    raiderx72's Avatar
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    did u use the old gas or drain it? some times it could just be bad gas... the gas now a days can sit to long before going bad... i had aproblem with my motocross bike like that just ran like crap.. drained the fuel and she ran good

  3. #3
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    check the pump..sounds like it may be binding... I wasted a whole bunch of time chasing that down on a pair of 150's till a little birdie suggested I pull the pumps..they were both thrashed..so now..I pass that bird call to you.

  4. #4
    Sounds like its running on two cylinders. Ride the ski or start it on the hose and get up the RPM's then check the temperature of each head/jug. A temp gun works best, if not you can lay your hand on it.I've found the front cylinder is 10 degrees colder than the middle and rear on the hose. If it has 1 cold cylinder it's your problem. Probably as simple as a fouled plug but could be ignition/compression/ or fuel issues. If you never have, pull the boots off and cut the plug wire back 1/2". It could also be the pump as suggested. This just happened to mine, when I blew my motor up the impeller backed off and it got into the housing binded up and died.

  5. #5

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    So what's the deal with cutting the boot back?

  6. #6
    PEVO's Avatar
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    Fuel filter? One of mine had a problem that sounded alot like that. You nail it, it tops out then would fall off to about 4500rpm & stay runnin, Peg it again same thing. If you stayed WOT, it would eventually die,...but then start right up. What i figured was happening was that the filter was maybe 1/4 clogged, but there was alot of crap floating suspended in the filter. This floating crap would at WOT suck up against the mesh screen & restrict flow...when you let off...this crap would fall off the screen & start floating again. Thus restricting fuel flow at WOT but not enuff to kill the engine at low RPMs Anyways a filter change did the trick!

  7. #7

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    Which fuel filter? The tank is a PITAS but the rear is a $5 filter at Advance Auto. Purolator match to the Fram.

    Mine had some nasty stuff visible in it. I've yet to attack the tank screen.

  8. #8
    PEVO's Avatar
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    Outside filter

  9. #9
    You cut the wire back, not the boot to give the plug boot nice new wire to screw into. Over time it can lose its contiunity and this ensures you have a good connection. I would check it like I said, if the fuel filter is nasty, replace it. Like you said it's a 5 dollar part. You don't want that junk to get past the filter and get in the carbs.

  10. #10

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    Mine filter had what looked like bugs in it...how the hell that got past the screen in the tank I do not know.

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