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  1. #1

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    Ultra 150 running away on trailer??????

    Hey you Ultra 150 Guru's. What in the hell is making my ultra 150 'only sometimes want to start running away on me on the trailer. Now I work on plenty of ski's but this one is a little wierd. I went through those big poxy CV Keihin carbs and cleaned them out properly.
    When I give it a little rev up ,maybe half the time it will start to take off.
    Definetely going lean , or drawing air from somewhere,but where???
    Both my ultra 150's an 04 and an 05 do the same thing.They only have 35 hours on them each and are stock.! (I've even had a STX900 05 and an 06 do it.) Must be something to do with these Big CV Keihin carbs.
    I turned out the low speed screw first a 1/4 then 1/2 a turn on each carb to richen up the low end. Now it seemed to stop it at first. Especially at 1/2 turn out. But then I started it the next day and away it went. So I turned the Fuel filter upside down and it stopped it. I thought this is the problem!
    Then it ran away again.
    Now you Kawi guys should know the answer!! as all the late model 2 stroke kawi's do it. Any help before I spend 5 more hours chasing this air suck!!
    For the record. On the water this boat actually performs good,Normal in fact, (speedo says 71 ish) (feels more like late 60's)but you can feel a little 3 second rev-up when you come down to idle after a high speed run, but obviously the load on the prop stops the complete runnaway.
    Thanks team
    Last edited by nz253; 04-19-2008 at 10:10 AM.


  2. #2
    btldigger's Avatar
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    Keep in mind the later model ultras had the smart steering. This should be on 03 and later. You can disconnect it, if you look at the middle of the carb rack you will see where the cable connects. You could also unplug the electrical connector from the actuator. This sound like what is causing your runaway.

  3. #3
    jonny5's Avatar
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    I agree it does sound like smart steering may be the problem which happens when the bars are turned and the throttle is chopped ...or somthing of that sort.

    On the trailer try running it with the bars straight and rap it a few times to see what it does...then maybe turn the bars to see if it starts to rev up.


    Not sure how you got to the screws which on the CV carbs are air screws not fuel screws so if you turn them out you are adding air to the mixture not fuel like a SBN. Think more like dirt bike carbs with these.

    They normally have caps on them....

  4. #4

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    Wow. Some good info there from you guys. The smart steer thing could be the reason. I did see that extra cable going to the carb and wondered why it was there. Although I did actually observe it alot making sure it wasn't moving causing the butterflys to open. I was observing all this when it started to run away again. and the cable did not move at all!! So I'll try moving the bars and see if this stops it.
    On the low mixture screw(interesting stuff again)A buddy told me to do this also saying it increases low and mid range power by about 20% by throwing more fuel into it. Which made sense.
    But to find they're air screws contradicts what he said. I havent run it on the water with the screw adjustment yet to test what difference it made. I think I will just to confirm what my buddy said.

    There were no caps on the screws they were just hidden in behind alot of white grease in the pockets. actually took me a while to find them .
    Anyhow thanks for the input guys. I'll do a test run this week and see what happens.
    Last edited by nz253; 04-19-2008 at 06:52 PM.

  5. #5

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    Hey you Kawi guys. Does the STX900 05 and 06 have the same power off steering function(smart steer) as on the ultra 150's

  6. #6
    btldigger's Avatar
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    Looking at the parts diagram it appears it does. I dont know this for sure but looks like it is set up simmilar to the ultras.

  7. #7
    jonny5's Avatar
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    No offense to your budy but he doesnt know what he is talking about. The CV carbs are air screws and have little affect on the tuning from what I have heard. I myself have not messed with these much yet ...but there is definatly not a 20% gain to be had by allowing more fuel to them especially on the bottom end. ....the low speed screw is really just for smooth idle adjustment.

    On these it's an overall mixture. PLus I dont know of any screw that will allow a 20% increase on any carb. THe CV carbs like on the kawi's have little adjustment till you mess with the spring,slide,needle,and jet sizes.

    On SBN type carbs the screws are fuel screws and also have a small adjustment range. Mainly for fine tuning.

    Sorry not being mean about your friend but dont let him tune your ski unless he knows what he is talking about. There are carb books out there so he could understand how SBN CV carbs work with the fuel curcuits. Dont want to blow your ski up..Then dont mess with them if it runs fine on the water.

    again not being harsh just striaght forward

  8. #8
    Had this problem on my 02 zxi, I beleive they are similar carbs, drove me nuts, turned out to be a leaky needle and seat in one or more of the carbs. If you swapped the needles when you took them apart to clean them, this is your likely culprit. The needle(s) are not seating correctly every time you bwap the throttle causing a small amount of fuel to get by into the low speed circuit.

    You can check the needle and seats on the bench by spraying with wd40 and popping them off to see if they gergle after seating. They should seat tight every time. Cost is about $100 for the trio of neddle and seats.

    The runaway could also be a vacuum leak somewhere else, crank seals, intake gaskets, carb base gaskets etc.....

    Jonny 5 is correct, these carbs have only idle air screws.
    Last edited by Chowski; 04-20-2008 at 10:37 AM.

  9. #9
    Hey guys, not an expert here but figured I would chime in. I have a 2000 Ultra 150 with a little over one hundred hours on her. Engine is completely stock, good even compression on all three cylinders, carbs have been cleaned and look good. It will go a solid 67mph on gps and runs great. My Jetski can run a bit lean while idling on the trailer, when the air temperature is cool...under 60 deg. F. In the summer when the water (river) and air temperatures are warm, my Ultra will idol right about where it should...+-1,800 rpm out of water and +-1,250 rpm in the water.

    I would suggest fine tuning the idol with the Jetski in the water, when the engine is at full operating temperature and the air temperature is within the factory jetting range...whatever that may be.

    Good luck.

  10. #10
    Quote Originally Posted by rjdenya View Post
    My Jetski can run a bit lean while idling on the trailer, when the air temperature is cool...under 60 deg. F. In the summer when the water (river) and air temperatures are warm, my Ultra will idol right about where it should...+-1,800 rpm out of water and +-1,250 rpm in the water.
    .
    Cooler air is more dense, and dense air will lean out air/fuel mixture. If it's just a little lean at start up, you should notice after a couple minutes of running in the water that it will settle back down once the carbs and intake warm up a bit.

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