i got a 2004 yfz 450. has pro circuit exhaust. white bros filter. air box lid off. it had a dyno jet kit installed in stage 2. i tried to put the yzf 450 dirt bike needle in it. i had serveral diffeernt jet. from a 168-175. tried the needle in position 3 & 4. could get it to run right. it would pop & cut out after half throttle like i was hitting the rev limiter. even doesnt when in neutral & holding the throttle. so i put back in the dyno jet kit just the way it was in before & its doing the same thing. i tried leaner jets & richer jets no help. any info would be great

 

Damn alota people seem to be having this problem....sorry I don't have the answer

 

sounds like your alittle rich, try running the needle in the second position from the top.

 

you'll likely get more answers at www yfz central com. No space in between but they wont let you post the address to the site in a post here. Guess they dont want you leaving here. Ive heard dynojet sizes their jets differently than keihin and other distributors do. Have you tried regualr keihin jets? Many compalints about dyno jet in particular, and most that do buy the setup get rid of it. I know of hardly anyone that has kept it in use after they bought it. Doubt this will help but here's what im running so far and im just a tad on the rich side on the last plug check.

175 main, 45 pilot, 2.5 turns on the screw, still running a lid, billet adapter and 2 stage foam filter, NCVQ needle on the 4 clip, HMF Ballance slip on. Elevation is around 5-700ft. If I remove the lid that will likely give me the extra air i need to lean the plug color up just a bit.

 

jet sizes comparison

The jets are also champhered different. I run Mikuni now. Kiehin & Mikuni are alike I think.

Most guys seem to run the needle rich 4th or 5th clip & adjust with the main jet.

 

yea...well i have heard that this is the problem(believe it or not) or stator is bad...check it...if it is, u can jsut get a new one for $105...i had that problem with my quad and i just soo happen to ask Hellbounds and he said that they have that problem with their YFZ and he looked at it and the stator was bad...so he changed it and it was jsut right...he said that people think that it is the jetting or the needle but he said most of the time it is not..sicne u have a jet and needle if it is the recommended size then u should have a look at that stator or have somebody else...

 

how do you check the stator?

 

u have to take the stator cover off for starters...and then u have to inspect it i guess.....not exactly u sure..u do the work urself? if so then i have no idea how to check that shnizle....but call this number 1-570-402-9000 and ask for mike or paul...that is Hellbounds....they open at 12:00 he knows his stuff real well and would be able to help u no prob! but i will try to find out like as of now

 

You can't run DJ jets with the yz450f needle, you need to get oem JETS to run with the yz450f needle!!!!!

 

I agree.

I think your jetting is wrong. Sometimes it is a bit of trial and error until you get it right.

Is the filter your using foam?

If so, Id start with
165 main
4th clip from top on the NCVQ needle
45 pilot
2 1/4 turns on the fuel mix.