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  1. #1
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    2009 crf250r jetting

    I am very frustrated.





    I put a new piston in a 2009 crf250. It has low compression and I was told the bike ran ****ty. I put a 2007 pistion in, its .2 or something a little lower compression. The valves are in spec, leak tested. Stock jetting is hard to start, starts and runs ok but has a flat spot.

    I have an fmf stage 1 jet kit with me, but its for a 2006. I tryed it anyway. Went to their recomindations, their needle 5th position, sf 2 turns out, 165 main. Starts easier but has a flat spot. Went to a 170 main and it still has a flat spot quarter to 3/4th throttle. Went back to 165 with the needle in the 4th position. Had the best power with this but it was giving me irrattic idle. It would take a second to get back down to idle after reving. Also the sc had to be turned out to 3. There is a 45 pilot in their now too.

    Please help! haha

    I'm assuming my problems are because im using the 2006 kit not the 2008/9. Correct?

    Maybe using the stock needle with some of the fmf main jets?

    Any thoughts?




  2. #2
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    Well, based on what you have said, I can see why you are having issues.

    You should only ever change one thing at a time and test.

    The main jet doesn't effect quarter to 3/4 throttle. that's needle.

    Neither needle or main effect idle, that's pilot.

    So, get the idle sorted out, then move to mid throttle and then once that's right work on your main jet.




  3. #3
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    In the morning, I am going to pull the carb and fully clean it all out and make sure the pilot is total free and clean. Then Ill go back to my setting with the fmf needle and fs and everything when it idles nice. Then I will need to sort out my mid throttle. Will this be combo pilot and needle or just needle. I dont have any other pilots here anyway.

    I had went one leaner from 5 position to the 4 position and I got more power out of it. However Then the idle was bad then, I had to go to 3 and a quarter turns out then.

    Maybe I should go richer instead. Or just try one more needle clip leaner to the 3rd position.

    thanks indy




  4. #4
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    my jetting options: (remote location)
    main 188,170,165,160,155
    pilot: 42, maybe find a 45
    needle stock- nnsu, fmf 2006 kit needle
    Leak jet: 70

    temp 85 F, elevation 1200 around, 65% humidity

    2009 crf250, bone stock except it as 2007 pistion signtly lower compression

    Can someone give me a base to start at?




  5. #5
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    your sudden erratic idle after moving the needle could have been an accidental bump on the float?? needles dont affect idle. go back to the stock jetting and start over. 3 turns on the screw tell me you need a smaller pilot



    m y   s i g n a t u r e:


    if you're gonna do something you'll regret in the morning its always best to sleep in

    if my ex-girlfriend was half as dirty as this president there wouldn't be an ex in her name

  6. #6
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    3 turns on the F/S means you need a LARGER pilot jet, which is very common on stock 4 strokes. Go up one size and set the F/S to 1.5 or 2 turns to start with. Once you get it running go warm it up and then turn the F/S in until the idle breaks up, then back it out until it smooths out, this will verify you have the proper jet. If it doesn't respond to input on the F/S it's too rich and you'll need a smaller jet. Once you get to this point you can go ride it around and fine tune the adjustment for best response, this should be within a half turn or so from where the idle smoothed out. Then do the main jet as it effects the volume flowing over the needle. Best way for most people to do the main when you have a 30 dollar spark plug you don't want to cut up is to just swap it out and use the butt dyno to see if pulls harder. The main takes about 2 minutes to change in the CRF. Warm it up and run it wide open through the gears a few times. Quickly go change the main a couple steps in either direction and you'll be able to feel if you're helping or hurting. No worries about going a little too lean while testing. Once you've got the main set you can play with the needle, which sucks to work with. My CRF was very responsive to needle clip position. I also did a few accelerator pump mods and ran a 45(I think) leak jet to clean up the throttle whack response. Timing, duration and aiming of the squirt are also important. Good luck and let us know how you make out!



    m y   s i g n a t u r e:


    Location: Erie, Pennsylvania

  7. #7
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    Quote Originally Posted by _JOE_
    3 turns on the F/S means you need a LARGER pilot jet
    whoops....what he said^^^




  8. #8
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    I called my mechanic freind yesterday before I went to work on the bike. He said using the 2007 piston was not really that great because even the little bit less compression would make a big difference. So for now until I could get a pistion here I did something crazy. I took the top end apart and put the OLD piston on (higher comp 2008 +) with the new rings from the 2007 piston. The part numbers are different but the guy said it would work. Maybe that guy is real good but is starting to get old and forgetful Because I'm not sure that was a great idea.

    Anyway, the bike was super hard to start. Got it started and it rode ok, stock jetting now. But the bike got way to hot. So I stopped everything and needed some time to think. Either the rings are a no go, or maybe my pilot is clogged.

    Took a break and guess what I found in a box. Two 2008+ pistions and a ton of rings and gaskets. Valves, stainless oil filters and some jets. What a find, I cant believe no one told me about the extra parts. Tore the bike down, put new piston and rings and gaskets. The cylinder looks good suprisingly after all that.

    Cleaned the carb out, my pilot seemed maybe a little clogged,not sure. Maybe it just donsent flow that much. I went to stock jetting again. Bike started right ip after all that. The idle was kind of up and down for a second. I played with the FS for a second and it cleared up. Did not have time to ride it yet.

    What a story so far. haha

    Sorry for the long post, thanks for help!!




  9. #9
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    I'm at around 1.35 out on the FS right now.




  10. #10
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    Quote Originally Posted by dirtbikr99
    I called my mechanic freind yesterday before I went to work on the bike. He said using the 2007 piston was not really that great because even the little bit less compression would make a big difference.

    NO, it doesn't.

    For what it's worth, I think you'd be well served if you stopped listening to this guy.



    m y   s i g n a t u r e:


    "another beautiful theory beaten to death by a gang of ruthless facts..."

    - Tom Hanna (Master Metalshaper/Nitrogeezer)

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