Jetting 08 yz450f


15 replies to this topic
  • racerxx276

Posted September 20, 2007 - 05:44 PM

#1

Has anyone changed the stock jetting on their 08 ? I just picked up mine and rode it around a bit letting it get warm, got a bit of backfire on deceleration .
I'm at 6000 ft, it should be running rich here , if it runs ok at sea level.

  • Wes Woodin

Posted January 09, 2008 - 07:45 PM

#2

Has anyone changed the stock jetting on their 08 ? I just picked up mine and rode it around a bit letting it get warm, got a bit of backfire on deceleration .
I'm at 6000 ft, it should be running rich here , if it runs ok at sea level.

Mine ran way lean here stock at 735 ft. Yours should run great there at 6000. Pop on decel is normal

  • roost271

Posted January 10, 2008 - 06:40 AM

#3

with a dr d pipe i am running a 48 pilot, screw at 1 3/4. i am in phoenix and temps are in the 60,s and about 25% humidity. runs much better off idle and the pipe helps it rev out more

  • Wes Woodin

Posted January 10, 2008 - 11:35 AM

#4

with a dr d pipe i am running a 48 pilot, screw at 1 3/4. i am in phoenix and temps are in the 60,s and about 25% humidity. runs much better off idle and the pipe helps it rev out more

Yeah I ran a 48 till I got the powerbowl, then I went up to a 52

  • todds924

Posted January 10, 2008 - 07:15 PM

#5

Yeah I ran a 48 till I got the powerbowl, then I went up to a 52


Hey Wes, Just curious if you have tried turning your fuel screw in all the way with that 52 pilot jet to see if it dies or still runs????

  • yz250o2

Posted January 10, 2008 - 10:50 PM

#6

What would that prove Todd? Is that a certain way to tell if your pilot is to lean or rich? If so can you explain that?

  • Ga426owner

Posted January 11, 2008 - 06:16 AM

#7

Has anyone changed the stock jetting on their 08 ? I just picked up mine and rode it around a bit letting it get warm, got a bit of backfire on deceleration .
I'm at 6000 ft, it should be running rich here , if it runs ok at sea level.


Guys some popping is normal ..... it can be almost eliminated 99%
you are correct you will need richer jetting - for 6000 ft
48pj or higher
170-172 mj or higher
2/3 clip
1.5-2 turns out on fuel screw

look at jetting sticky 06-08s should all be close

  • grayracer513

Posted January 11, 2008 - 07:15 AM

#8

you are correct you will need richer jetting - for 6000 ft

High altitudes require LEANER jetting than low altitude.

But you're right about decel popping. If you get rid of all of it by richening the idle circuit (assuming your exhaust doesn't leak air) then what you have is a bike that runs too rich with the throttle closed. "Some" (a very precise quantitative term) is normal, and an indication of a correctly calibrated idle circuit.

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  • Wes Woodin

Posted January 11, 2008 - 08:01 AM

#9

Hey Wes, Just curious if you have tried turning your fuel screw in all the way with that 52 pilot jet to see if it dies or still runs????

Todd never saw this one. It dies.

  • grayracer513

Posted January 11, 2008 - 08:04 AM

#10

It would, even if you had a 70 in it. Seating the screw should close off the pilot circuit as it leads out to the discharge port.

  • Ga426owner

Posted January 11, 2008 - 01:24 PM

#11

High altitudes require LEANER jetting than low altitude.



yep I am backwards....again :banghead:

Guys some popping is normal ..... it can be almost eliminated 99%
you will need leaner jetting - for 6000 ft
42pj
160-165mj
3/4 clip
1.5-2 turns out on fuel screw

  • todds924

Posted January 11, 2008 - 05:12 PM

#12

Todd never saw this one. It dies.


Let me re-phrase that. " how close to fully seated can you get it before it dies?

  • yz250o2

Posted January 11, 2008 - 06:24 PM

#13

Man my bike when fully seated does not die. Is that bad?
48 pilot

  • grayracer513

Posted January 11, 2008 - 06:36 PM

#14

Is that a stock, or aftermarket fuel screw you have there?

  • yz250o2

Posted January 11, 2008 - 06:59 PM

#15

Aftermarket GYTR screw.

  • grayracer513

Posted January 11, 2008 - 08:41 PM

#16

That's not too likely to be the problem, but you might check the length of the screw from the end of the threads to the tip. There are two different screw lengths, one for yours, and a shorter one for some much earlier models. If you have one that's too short, the thread will bottom, but the tip never reaches far enough to seat, or to meter the fuel correctly. Probably not the case here, but you don't know unless you check.





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