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Thread: Eratic running

  1. #1
    yankee817299's Avatar
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    Eratic running

    Well, I got the stx-r back in the lake this week after replacing the crank shaft and doing the top end over the winter. I went through the routine break-in with pre-mix and nothing above half throttle. The ski ran fairly well through this. It has Factory Pipe triples on it. I kept feeling the water coming from the pissers and it never got hot, just stayed luke warm. Kept the ski at 4000 rpm's and under for a tank of gas. The plugs are staying a nice light brown color, compression is 120, 120, 120.

    Today was the day to cut loose. The ski would rev to 4000 rpms, then hesitate and jump to about 5.5 or 6000 rpm's and take off. I am a little worried because this is how it acted last summer before it seized on me. I am having good water flow from all 4 pissers, starts easily when cold or warm. The ski is new to me last summer and seized on my first run with it due to my in-experience. While doing the re-build, I found alot of sand in the blown cylinder pipe, cylinder, and water line filter. I probably emptied a full cup or better of sand from the different components of the bad cylinder. I thought this was pretty much the cause of the failure, but am not completely sure now. I have another stock stx-r that has a very smooth and responsive throttle and I would love for this triple pipe to be the same? Am I asking for too much? Any input to point me in the right direction would be nice.


  2. #2
    btldigger's Avatar
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    I would watch the plug chops just to play safe and to make sure the carb tunning is right. I dont think your going to be seeing smothe power from a tripple pipe. I run caughmans on my ultra and it comes on the pipe at 4k. it is like throwing a switch. Its either on or its off.

  3. #3
    jonny5's Avatar
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    Pipes really are a on or off type of ride hard to just cruise alot. If you add alot of water they tend to be less jumpy with the jetworks....

    you could richen it just a little....but it's a tunning ting also with tripples.

    Not sure but did you pressure test the pipes when they where off???

    ANyway hope the ski gets going soon... If you have about 10mins on it then your good to run just the oil injection unless it's a sleeved motor then run it a little longer.

    Most damage accurs when under hard load like turning hard and punching it. Going striaght alot is not really that bad unless you go WOT to long. Another thing is that somtimes depending on the timing of the pipes and cdi you can experiance a lean condition around 5000 to 6000 which is usally a nice cruising range .....but pipes are not made to cruise so if your in that zoon and it stuck be alert and listen to your motor. It does tell you things by the way its running.


    Hope this helps

  4. #4
    yankee817299's Avatar
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    That makes sense about the pipes being off or on. It will cruise right up to 4000 rpm's, then thats about the spot the pipes kick in with more throttle. The carbs are stock with the recommended jetting from Factory Pipe and the updated cdi. I did not pressure check the pipes? How would this be accomplished? Also, one minor problem I noticed when re-installing everything. The throttle cable has about 1/8th inch play in it. It is good at the oil pump end, but loose at the throttle end. At wot it does not open clear to the stop. I adjusted it out as far as possible. Is there an adjustment on the throttle lever end also? Can the factory pipe style cable still be purchased if needed?

    Jonny and digger just want to let you know that you both were very helpful in assisting me with this re-build. I appreciate everyone's replies to the posts I had through this.

  5. #5
    yankee817299's Avatar
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    Would running pre-mix in the tank help in preventing any damage due to it running lean in the 6000 rpm range?

  6. #6
    btldigger's Avatar
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    Actually not, It will help with wear since you are turnning higher rpm. Adding oil means there is less fuel. Another shim under the slide needle would help it. Alot of us ultra guys run 100:1 premix along with the oil injection.

  7. #7
    yankee817299's Avatar
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    When you say add another shim under the slide needle, are you talking about the needle valve in the carb? If so, would that be adding another washer behind the needle?

  8. #8
    btldigger's Avatar
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    What im referring to is the cv slide. If you pull the diaphram out then look down the top side you will see a plastic nut. Remove it and remove the needle, there will probably be a washer under the needle. You can add 1 or 2 more to make the neede open quicker and add more fuel.

  9. #9
    yankee817299's Avatar
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    Should I do all 3 cv slides the same?

  10. #10
    btldigger's Avatar
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    Probably yes but you need to have a look at the plug chops to see how its running. Then after is had 4 or 5 hours of run in time you could pul the heads and check out the piston wash.

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