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03 kfx400 questons ??

8285 Views 16 Replies 6 Participants Last post by  jonboy
how do i know if my cdi box is bad ?
does a performance cdi need the carb to have a stage jet kit or is it one or the other ?
who makes a good performance box for my quad ?

i have searched for these answers but nothing yet . i know i need a carb kit for my quad but im also wanting up get a performance cdi box too . are the jet kits like a carb rebuild kit or do i need to buy a jet and a rebuild kit ?

any help would be great . thanks robert
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Typically if your CDI is bad It will not fire or have a really intermitten spark. The Best CDI's are Dynatek, however they are costly. The majority of the restof the aftermarket CDIs are made by Procom and have a strong reputation for failing very fast. No you dont need to rejet for a CDI. But without getting stronger valve springs such as the DRZ400 springs I wouldnt get a CDI that allows more than 2000rpm over rev. The Jet kits are not a rebuild kit. They are usually just jets and an aftermarket filter. Rebuild kits are usually new seals, o-rings, bushings for the flap and needle and diaphram assy. The adjustable clip needle is the only thing worth a crap though. If your carb needs a rebuild, you may want to look into getting a FCR39 off the YFZ450. It is way more responsive and will out flow that 36mm stocker any day.
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so a stock 44mm carb off of a yfz450 will be much better than a stock kfx400 carb ? i just looked them up and they are pretty cheep .
It should be a 39mm unless someone had it bored. I dont think they could get bored to 44mm. Yes it would be better but, it will take some modding to get it to work. like new boots and such. You could even use a FCR37 off of a crf250 and it would be better. It all depends on what you want. If you plan on getting cams or doing a bigger bore then definately get the FCR39 off the YFZ. I can email you all the details to make it work. Or even try to get the info stickied here. You'll have alot of time into it and possibly money too but like I said it is all in what you want. I thought it was worth it for the money on mine, but I also raced mine for almost 4 yrs. It definately was the best mod I've done. You need to check out SuzukiCentral (Powered by Invision Power Board) and do a little research for yourself to decide whether you want to do it or not. Just go to search and type in FCR. The whole idea came about from Yoshimura as the did tons and tons of research on this motor on the DRZ400. That is why all the mods came about so fast to the Z400 and they smoked the other factories on the national circuit when they came out.
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hell yea . im looking at one on ebay right now . he says its a 40mm bu in good shape . im also looking at a dynatec cdi rev box .

right now the quad drives great till i get on it and when i let off it dies . i have been playing with it but no success . dam thing has a piss load of power as long as your in it . just putting around it wants to die .
when you jet a carb. how do you tune it to run properly?
I usually start with the pilot jet and get it to idle correctly. I adjust fuel screw in to see if it dies by running it in. If it dont die when ran all the way in, then go down in size on the pilot. Once I get it to where I think is good I adjust the Fuel screw 2-2.5 turns out from seated and then check with idle adjustment screw and blip the throttle a few times to see if it goes back to idle or if it hangs. If it hangs I adjust the fuel screw a bit more until it stops. Then I move to the main jet. The main jet requires a little less work. You ride the bike and get it up in the top end and see if it cuts out or dies on top. If so,then go up in jet size to a bigger size until it stops. If it doesnt die but pops and back fires on the decel then go down in jet sizes until it stops. Keep some new spark plugs handy because you may foul some and you want to start checking your plug when you think your close. It will tell you where you are by the color. The needle is a bit more tedious because of the location but usuallly easy to dial in. You'll need to ride the bike and get into the throttle slowly to get to your top end if it sputters on the way to top speed the you may have to start shimming the needle or move it up from the seat to get more fuel in your mid range. It normally doesnt have to get moved much. If you have an FCR then you have the AP to deal with. First do the AP o-ring mod. and then move to the leak jet. It is a PIA to dial in. I eventually kept getting to the point that I would get smaller and smaller in jet size until I finally plugged it and what do you Know, It came out of the hole prefectly. Hope this gives some insight to some of you that are new to jetting and, if there is anything I left out some of you other guys jump in. Or if you do it differently. Put it down because your way may be better or easier.
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Great info jon :rock::rock::rock:
damit man . you really know your chit . this is good info to have in the future . thanks
sounds like some tough work to do. i'll message you so i dont start a new thread
No problem. Its not tough at all. Can be arbitrary at times but once you understand how your carb works, like which jet controls what function, you'll know directly where to start.
Kawasaki KFX400 Choke/Jetting Problem


I just recently purchased an '03 KFX400 and have been making minor mods to optimize performance. I have a K&N with a precharger and a White Brothers exhaust. After purchasing, it ran fine, but then I wanted to change the jetting or at least check it to verify that larger jets were installed to account for the air and exhaust mods. When I disassembled the carb, I noticed the main jet was smaller than stock so I change it to be stock (thinking this would give me a little boost). The second time I rode it ran like crap. It would cut out on me and it finally just died and stopped starting. I removed the spark plug and found that it was completely black, which I assume is too rich. I also realized that the choke had been stuck in the open position due to corrosion where is connects to the carb. I am currently cleaning out my carb and fixing the issue I have with the choke.

Assuming the choke was on all the time, would this first account for the smaller jetting? And second, once I get everything back together, should I stay with the stock jetting or should I be able to increase that as well?

Please let me know if more information is needed.
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Yeah, Sounds like some dope didnt wanna fool with repairing the choke. Its amazing how some people repair things. Lol. Get a push/pull choke off ebay for it and eleviate some of your issues that occur with the cable setup. Yeah with those mods, the main will need to be larger. Depending on your elevation but , with the mods you stated you should have around a 160 main. Is the lid off the airbox?
After removing the choke from the carb we were able to free it up. I am putting my carb back together today and I think the choke will be working fine.

The lid to the air box is currently open and I think the largest jet I have is a 150.

Any other suggestions to get a boost would be cool.

You should be able to buy individual jets at your local bike shop. just tell them the size you need.
I must admit I am a little new to the KFX's myself, but from my experience with snowmobile carbs it seems a little high. I believe the stock main jet is 130 in the KFX 400. Would a K&N intake and aftermarket exhaust really need a 160 main jet? Is this just to be on the safe side for her, to ensure she doesn't blow it up going to lean? What kind of hp gain's are the intake and exhaust giving her? Thanks.
The z400 motor is very suseptable to slight mods. You'd be surprised how much just opening up the airbox would do. Just changing the factory intake tube with the 400ex is worth approximately 2-2.5hp on a dyno run.
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