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  1. #1

    900 STX Running Issue

    Hey guys, I have a troublesome 2000 900 STX, ran great before it sat this past winter. Brought it out for this summer and it wouldn't start without a carb clean. Now, it fires up and runs, idles ok for a short while, backfires a little when I get past half throttle, and then dies. This is what all I have done and checked: completely disassembled carbs for cleaning(twice), drained old fuel and replaced with fresh 93 oct, replaced spark plugs, checked reeds, cut spark plug wires back about 1/4", checked wire harness for bare wires, and some other small things. Took it to the water for a test run, it was real boggy off the line, seemed to be running a little better than if it were running off of two cylinders. Would only reach about 35-40 mph. I let off the throttle for another start from idle, was real sluggish off the line again and then started running like someone was playing with an on/off switch going between running on 2 and 3 cylinders. I brought it in and called it a day. I pulled the top from the coil box and everything looked good. A little rust on the started solenoid but I don't think that will cause a running issue. Seems to be getting over fueled as well. I just don't see how this wan't just a simple carb clean from sitting over the winter. Any suggestions will be great. Thanks...


  2. #2
    DPeteLand PeteSkeet's Avatar
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    possibly carbon...?

    you might even just want those carbs tuned first... an improper fuel mix in each piston can cause weird things...... buuuuuut,

    it sounds like carbon buildup to me... the problem i have with the stx * i own a 2000 kawi 900 stx aswell * is that the carbs.... if not properly adjusted FROM THE START will cause carbon to buildup in the pistons.... thus causing the backfire issue or even a deiseling effect... my best bet would be to take off the head... if there is carbon buildup present take a handpad about 7447 grit * looks like the thing on the rougher part of a sponge..... i can get a pick if you like... sorry im so retarded today... cant remember what their called* cand start to take off the carbon in the head and ontop of the pistons... u can also use that to take off the silicone gasket film thats left over on the eam of the head and upper block of the motor..... then you cna proceed to taking it to a marine shop to get those carbs retuned... that way it wont happen again.... either that ot the oil injection went bad or is too strong... check that oil pump to be sure... u dont even have to start the motor... just unplug the end going to the motor and let the engine turn. if even a little bubble forms then your ok.. if it seems liek its going to fast then consult a real marine mechanic ooor just convert to mixed.. 40:1 haha....


    other possibilities... replace fuel andoil filters... lines shold be ok though

    i couldnt see any other problem with the motor besides carbs.... but u re did so they should be good.

    thats just my two cents worth i hope it helps you out! if you suspect other problems then i would pursue those aswell... bur seeing as how the carbs are rebuilt...




    infact ive had this happen to my dirtbike.... it was a carb not being tuned properly!!!!! TUNE THOSE THREE CARBS!!! *OR TAKE IT TO A MARINA AND HAVE THEM DO!

  3. #3
    DPeteLand PeteSkeet's Avatar
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    EMORY CLOTH!!! thats what that abbrasive material is!

  4. #4
    Thanks for the reply. There are no adjustments on the carbs. There is a low speed on each carb but they are all covered with caps. The carbs would have to be separated to drill each cap and then resync...pain in the arse. I pulled the spark plugs several times and it seems like it's being over oiled. Can an oil pump go bad and produce too much?

  5. #5
    PEVO's Avatar
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    Quote Originally Posted by 2weelz View Post
    Thanks for the reply. There are no adjustments on the carbs. There is a low speed on each carb but they are all covered with caps. The carbs would have to be separated to drill each cap and then resync...pain in the arse. I pulled the spark plugs several times and it seems like it's being over oiled. Can an oil pump go bad and produce too much?
    Do all three of your sliders on you CV carbs work in sync? One may be lagging behind the others or hanging up. Did you rebuild the fuel pump? change the fuel filter?

  6. #6
    DPeteLand PeteSkeet's Avatar
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    Quote Originally Posted by PEVO View Post
    Do all three of your sliders on you CV carbs work in sync? One may be lagging behind the others or hanging up. Did you rebuild the fuel pump? change the fuel filter?

    that could cause an oil over.

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