08 yz450f jetting needle and leak jet Question

5 replies to this topic
  • supermo26

Posted March 02, 2016 - 11:27 AM


I have read alot about jetting on the forum. I'v done the o ring mod but havent rode hte bike since. I ride trails and desert. I don't race.


My question is JD Jetting doesn't sell their needle by it's self. Is it wort it to get their jetting kit or should I just change leak jet and main as required for my altitude and weather and a new exhaust?


Looking to clean up some low end bog after getting exhaust. I don't want to spend money I don't need to, but everyone raves over the JD Jetting kit.

  • grayracer513

Posted March 02, 2016 - 12:34 PM


I wouldn't have done the O-ring mod, but that's OK.  They're easy to cut off if you decide you've over done things. I also don't use JD needles because of the difficulty in comparing them directly to Keihin parts.  My preference.


An '08 tends to benefit from reducing the diameter of the upper needle, above the taper.  This richens the transition from the idle to main circuits.  Use an NFPP needle (5TA-14916-PP) in place of the stocker, and try that.


As to the leak jet, you should leave that alone until you see how the bike behaves with the O-ring in place.  If you stay with that mod, you may find you need to go considerably larger on the leak to avoid stumbling from excessive richness during slower throttle maneuvers. 


I know this bike, and it ran great from sea level to 3800 feet at least: http://www.thumperta...99#entry4459899


Also read: http://www.thumperta...f/#entry3596648

  • supermo26

Posted March 03, 2016 - 08:50 AM


grayrace513, I read a lot of your post and I thank you for replying to my questions.


I'm currently in Klamath Falls OR. and we are at 4100 feet. I also ride at Johns Peak that is lower and I have a "race" or ( ride, for me because I'm not a racer.) in Virginia City that is 6100 feet. Will your recommended needle still be ideal for altitude correction?


I'm not apposed to scrapping the o ring. I like things to work as designed. I just figured I'd try it out.

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  • grayracer513

Posted March 03, 2016 - 10:15 AM


The needle will still likely help your tip-in hesitation, but you might need to reduce the jetting for your altitude.  A rough rule of thumb is to go down 1% per 1000 feet of altitude gain.  If you take Todd's average elevation as 2000 feet, and yours as 5000, that suggests a 3% reduction.  His 165 would be reduced to a 160 (165 x 0.97), and his #43 pilot to a 42. 


Try it out with the O-ring mod.  At least you didn't wire the thing.  There is also a heavier accelerator pump drive spring available from sources like Merge Racing, JD, etc. that does the same kind of thing that the O-ring does, but is obviously a "cleaner" solution. 

  • supermo26

Posted March 20, 2016 - 11:46 AM


O ring and DRD pipe did wonders but I want to cut off the o ring and try the needle and pilot jets as you mentioned above. If I buy a 42 and 43 pilot and a needle , I will still spend less than jd kit. Should I do the needle first or the pilot? Bike  ran good with no bog, my only concern would be if I am running lean (hot header pipe). I'll re check fuel screw after a warm up before next ride. Last time I turned the fuel screw in, my head pipe was glowing bright red in a hurry. I'm currently at 2.0 - 2.25 turns out.


Also an 05 yz450r has been stalling even when when pulling the clutch in. Guy who's riding it tends to stall a lot, but He is not a new rider. I'm thinking it is carb related because he changed a leak jet a while back because previous owner had it stripped out. He did use a orange rubber o ring that we use for aircraft tire valve core assemblies. The tent to swell in the solvent tank.  

  • grayracer513

Posted March 21, 2016 - 06:21 AM


The pilot jet and needle work in in concert with each other.  I'd use the 42 considering the altitude at which you ride.  The header getting glowing hot is a feature of the breed.  An elevated idle speed will contribute to it, but it's pretty normal after 40-60 seconds of idling to see the pipe turn visibly red in low light situations like twilight or in a lit garage at night.  At that point, the pipe is at about 800 degrees.  Exhaust temps run at around 1200-1600 degrees, so you can see where the heat comes from.


Regarding the '05, stalling on a throttle chop is caused by an excessively rich pilot jet more often than not. 

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