I'm looking for all the right answers on how to rejet my carb for the 400ex. I installed a new k&n filter and fmf megamax exhaust with all discs installed. Please tell me how to rejet CORRECTLY (if necessary).

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Steve Small, 00' 400ex, 00' 325 Trail Boss for the Mrs.

 

steve, contrary to some opinions I've heard jetting isn't brain surgery. the first and NECESARY (caps intentional) thing you'd better do is to go two main jets fatter than you previously ran.If you aren't certain whetheryour present main is stock, pull it & check the no. on it. Altho you may have bought the bike new, it doesn't mean the jetting is stock. Your elev. may have caused the deaLER TO alter the jetting, usually the main.After determining what you have then you can buy two fatter jets & install the fatter of the two.The reason behind this is, in case you would want to go to the mountains or a higher altitude, you'd have a leaner jet to adjust to the elev. change.
now, you've got that done so you won't have any burned valves or other heat related expenses from running too lean,we can address the next item:find a good open spot where you can run the bike at 3/4 to full throttle, not necesarily in 5th but at above throttle setting in a lower gear for a mile, more or less. Any backfiring, missing, cutting out? You're still too lean..go up one fatter on your main. with your current level of breathing mods, tho, the above symptoms would be doubtful.If none of the above, then you have rejetted for top end.. simple,huh?

Now, next question: what's your riding style ? moderate recreational, fast trail riding, aggresive tight woods or trail? if you do either of the latter two your needle jet is probably right on in the normal center slot. If you tend to do a lot of slow to moderate (read 20mph or less), then you may need to raise the needle one notch if you experience any lack of throttle response.This allows more fuel to enter the carb at 1/3 to 3/4 throttle. In all the years I've ridden I've never had to change the pilot jet so I wont even go there. Basically that the nitty on rejetting.
Keep in mind; the pilot jet's job is from idle to approx 1/3 throttle..the needle jet from 1/3 to 3/4... the main jet from3/4 to full throttle. Since not carved in stone these figures sometimes overlap, but not much.
2 basic rules in any alteration of any thing: never change more than one thing before testing then go to another if need be.
Good Luck, & be sure to tighten the boots on your carb after jetting

Cal, the Az hardpacker

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join the Blue Ribbon Coalition online at www.sharetrails.org



[This message has been edited by hot_shoe_cv (edited 08-21-1999).]

 

EXtreme, I'm unfamiliar with the 400 EX's specific carburetor; but, I assume basic principles apply.

You've received good advice in Hot_Shoe_cv's post on this topic. I would add:

The absolute certain do-it-yourself optimum carburetor jetting method, a technique taking into account your own quad and its unique equipment and characteristics, the altitude, temperature, humidity (and phase of the moon; just kidding!), is:

Plug Reading

I'm not going into any "smart talk" on the subject (there may be Arctic Cat riders present); you can learn about "plug reading" and other carburetor kinks on the Web (try "Motorcycle Carburetors" on Web Search) and in books.

One source of a lot of information on carb tuning in general in a short Web posting may be found at

http://www.icnetx.com/speed/jet.html

Good luck!

Tree Farmer



[This message has been edited by Tree Farmer (edited 08-21-1999).]

 

Verry good hot_shoe_cv.You get a cookie.
I think I may print that.

Actually Hondas are jetted for the state they are shipped to.Thats what the rep told me.

EXtream I'm still waitting on UPS.Will update.