Carb re jet problem

[The 400ex kid]

Ok here's my problem I have an 03 400 ex .......well my problem is I have a red graydon pro line exhaust and I was wondering if any body knows the jet sizes and and adjustments for 1900 feet above see level ...... I would be extremely appreciative for any info thanks

[CJM]

42 pilot, 150 main.

[The 400ex kid]

42 pilot, 150 main.

What about mixture screw and needle position

[CJM]

What about mixture screw and needle position

sorry...

3rd clip and 2.5 turns out fuel screw.

[450rtt]

before we can recommend jets it would be wise to know if you are running with the airbox lid on or off. That is a key factor in jetting along with exhaust.

[CJM]

before we can recommend jets it would be wise to know if you are running with the airbox lid on or off. That is a key factor in jetting along with exhaust.

This thread is 2 months old....

kthxbai

[450rtt]

if somebody reads this 5 months or 5 years from now and takes those recommendations to heart i would hope they would have the knowledge to know whether or not a lid was present, it makes a difference in jetting, a substantial one at that and i think the question should have been asked before throwing jetting specs out there. Airbox lid and exhaust are the 2 main things that will effect jetting.

[CJM]

if somebody reads this 5 months from now and takes those recommendations to heart i would hope they would have the knowledge to know whether or not a lid was present, it makes a difference in jetting, a substantial one at that. just trying to help.
right......you just HAPPENED to find a post 2 months old somehow...just like magic and Im the only other poster in it. Stop trying to start trouble.

[450rtt]

For example if i was running an exhaust with the lid off i would be closer to a 165 main jet, with a 40 pilot, and 2.5 turns out, 3rd clip on the needle. That's just my 2 cents. It is very important to know if the lid is on or off in order to give proper jetting recommendations. Really not beneficial to throw a number out there without information like this.

[KKiowaTJ]

Stock they need changed to a 150 main and a 40 pilot. But as it is, Most 400's are one in the same and usually the only factor is the main jet and a/f screw. More so if the person didn't have a box lid, He would have mentioned it. But for the most part, And you can do a search, 150-160 main and a 42p is the most common jetting set up regardless unless a built motor. After that its fine tuning with the clip and a/f screw.

[450rtt]

I don't really need to do a search i've jetted about 10 of these in the past, fact is air flow is the #1 most factor that will affect jetting. Altitude, exhaust and air intake are what determine jetting sizes. It makes one heck of a differece as to whether or not the lid is on or off. The 400ex come stock with a 148. If you pull the lid and throw a slip on on there you will need good jump in jets. I personally would not give jetting advice without knowing if the lid was on or off, it does make a difference. No motor is the same and the main jet and AF screw are not the only factors.

[CJM]

So what your saying is that my friends 400, which was totally stock then went to 11:1, cam and open airbox with a stock exhaust shoulda been what a 170 main??? I mean we put a 155 in there and what do you know it was way to rich..150 was perfect.. Or would the same setup on another persons 400 had a 195 in there??? I mean since no motor is the same?????

[450rtt]

so you went up 1 size on the jet, from a 148 stock to a 150 with 11:1, cam and open airbox? personally i've never run a stock pipe with mods like that, why would you? but i'll say my 11:1 ran a 178 main jet. just proves that not all motors are the same. and it also proves exactly what i was explaining, intake and airflow thorugh exhaust are the 2 biggest factors in jetting. 150 sure seems lean for your friend but hey if it runs good you must have it jetted perfect.....till she blows.

[JOHNDOE83]

so you went up 1 size on the jet, from a 148 stock to a 150 with 11:1, cam and open airbox? personally i've never run a stock pipe with mods like that, why would you? but i'll say my 11:1 ran a 178 main jet. just proves that not all motors are the same. and it also proves exactly what i was explaining, intake and airflow thorugh exhaust are the 2 biggest factors in jetting. 150 sure seems lean for your friend but hey if it runs good you must have it jetted perfect.....till she blows.

In my opinion and from taking jetting advice from the largest jet seller/manufacturer there is. I would say stock factory EXs need at least a 160 main jet and a 40 pilot, there was and still is stock bore EXs with carb,exhaust,intake mods, and cams running 200 size main jets.

Go big or go home in the jetting world is what needs to be done no matter what for maximum performance, its NOT to lean until it stutters out from to much fuel. Once it stutters out like a rev limiter at full throttle back down jet szes until it fully revs out.

My .02 cents, and also reccomended by jetsrus.com