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HELP bottom end bog

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Ok guys im new here and all that stuff but I just picked up an 07 kx250f had a bottom end bog but ran decent and idled good I had to replace the air/fuel screw now it won't idle and i can't get it tuned for shit maybe it's the new air screw? Any help is greatly appreciated

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A little more detail for you:

  1. close the fuel valve, loosen the clamps, tilt the bottom of the carb out towards you.  Bowl sticking out the side.
  2. Go fishing in the fuel screw hole for the oring, washer, spring on end of 16014. Clean out the hole, then set the fuel screw at 2 1/4 turns open from seated.
  3. unscrew 16049 and 92009 and clean/clear/rinse out any crud or sediment in the bottom of the bowl.
  4. while you have 16049 off, remove the pilot jet 92064, blow it clear, take note of the size number on it, put it back in.
  5. check that the hot start plunger 16016A and port are clean, that the plunger moves freely in the port and that the boss 16012 when screwed on is sealed to carb body so no air leak (sucking in air) possible.
  6. next tilt the carb the other way to get at the other stuff
  7. take the top cap off and put the jet needle clip 92170 in position second slot from the top of the needle
  8. Open the bottom cap 14024 to check the condition of the diaphragm 43028, clean it and put back in
  9. set everything back in place, snug the clamps, open the fuel valve, 
  10. remove the seat, remove the air filter, look into the inlet of the carb
  11. turn the idle speed screw 16021 so that at zero throttle the opening at the bottom of the slide is 3mm (just shy of 1/8"). Example, put a 1/8" drill bit under the slide, screw in until the slide just begins to lift off the bit.  Remove the bit, of course.
  12. Wack the throttle while looking in the carb throat.  Adjust the linkage from 46102 at 16170 so the accelerator pump fuel squirt just barely misses the slide as it rises when throttle is opened.
  13. Replace air filter and seat.
  14. Pull the choke 16016.  Go for a start.
  15. Increase idle speed, screw in clockwise (16021) by 1/4 turns between tiring tries until it starts.  Do NOT pump the throttle unless it is running, that will flood it.
  16. Once running.  Push the choke in.  After it is nicely warmed up, then set to comfortable idle speed and tuning of the fuel screw.

If those things do not sort it out, then pull the carb for full disassembly and cleaning, including installing NEW pilot jet 92064 size 42 


My method for tuning the fuel screw ... Get the bike warmed and idling at the speed you like.  Pull the hot start lever and listen to what the engine does.

  • IF the idle fades off, drops, maybe even dies, then it is lean.  Open the fuel screw 1/4 turn out.  Try again
  • IF the idle stays the same, then is it still on the edge of lean.  Open the fuel screw 1/4 turn out.  Try again.
  • IF the idle picks up 200ish rpm and holds steady, then it is perfect.  Stop
  • IF the idle picks up, perhaps stumbles a moment, then picks up 200ish and grows even more, then it is rich.  Close the fuel screw 1/8 turn in.  Try again.
  • IF you do not seem to be getting anywhere, then your idle speed is too low, out of tuning range.  Increase the idle speed screw at least 1/4 turn.  Start over.
  • Last - readjust the idle speed to where you like it the most.  The go through the fuel screw tuning here one more time.  Then you are done.

Hope that helps!



Edited by FaceDeAce
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Cool man thanks I pulled my aftermarket air screw and the needle is bent and looks like somebody took sand paper and filed one side down put the factory one back in and I'm still lean im gonna get another screw and change the pilot

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