Hey Guys,

I have a 2004 KFX400 - all stock that I picked up about 3 weeks ago.
Had to replace both front and rear axle bearings right off the bat, repair/replace waterpump internals clean out varnish-filled carb. I noticed that my pilot jet holes in the throttlebody were very clogged so I sprayed them through the jet until a dark colored ooze came through and kept going until it was clear. Put it all back together and it fired up great. So yesterday was the first real day I could go out and ride.

I noticed that when going fast in the high gears, I would lose throttle response trying to blip up the rpms and some times it would just stall and coast to a stop. It would take some time to get it started again by trying to change the petcock to primary/on on/primary but seemed that it had to sit about 5 min. to start again.

at the end of the day, I had to keep the choke on to get it to start and make it back home.

I have no idea what to do anymore - Carb is very clean, seems that it can't keep enough gas in it when at high rpms.

Any ideas?

Did you clean out the fuel inlet valve well when you did the carb/jetting clean? Sounds like that might be it...

Hmmmm...

Trash might still be in the carb...clean clean clean and take compressed air and blow the jets out..

Are you sure it doesnt have any aftermarket jets made to the carb?

Everything needs to be right in the carb EVERYTHING in order for it to perform well...

Fresh gas and make sure the tank is clean...

But IMO it sounds like a carb issue for sure...oh by any chance did you mess with the tps or just unplug it? because if you did that could and might be a problem..

Give me some more information and I will see if I can help..

PS: Glad you got it running tho..

One last thing...

By any chance was you LOW on fuel? If so...........switch it to reserve lol because several times I been at full throttle and blah blah blah and was like wtcrap...and then was like shoot I am about out of gas and had to choke it to get it home after reserve was gone...lol I know that sounds nuts but I had to ask...

Lastly, did you go through any water....sometimes after I spray mine off water gets down on the plug and she sputters like crazy...this prob isnt your case BUT check it and also check to make sure your plug wire is SNAPED down all the way click click click...

sounds like you might need to rejet the carb. I live here in florida in summer wen its hot out i will sometimes get water in my tank if i dont fill it up all the way i guess its from condensation but thats just a thought, water in gas will make your bike run like crap lol, put some stabil or water remover in gas it might work.

no intake leaks ? loose boot ect.

It's an 04 so there is no TPS plug on the carb. I did go through some water and the front holeshots really throw a tidal wave all over the place but that was later in the day. The Jets are all stock and clear and I filled the tank with 93 that day I got it running. Air/Fuel screw still has plug in place. I made sure that the intake and airbox connection were tight and secure. I completely drained the tank too when I cleaned the carb and threw out the old gas.

I will take the carb off again and check the fuel inlet which I didn't clean the first time. I will also check the gas cap to see if it is causing a vacuum and not letting fuel get into the carb. It ran really good for about 85% of the day. It would stall while moving and have to sit for a couple minutes before it would start again.

At least I know it is not anything really serious and is either tank - carb - spark related. Troubleshooting is almost as fun as riding! I plan on ordering the Lexx slip and a new filter. What would be the best Jet/fuel screw position combo to start with with stock header?

save yourself the money and just get a used full system. they sell them all day for 200$ in the for sale section.

I know people have posted these "listen to this and tell me what it could be" videos before.

But here is mine... Valves?chain?

sounds like a cam chain. but its hard to tell at idle. what happens when you try to rev it up a little?

Heres one with reving it...sorry for the bad quality

I'm having the same exact problem with my 03 z400, except mine is not rideable at all. Let me know if you figure the problem out, i'm all out of ideas!

wow thats weird... when you rev it the knock stay almost the same... if it were cam or valves it wouldve ticked faster along with the engine.... let me know if you find anything...

idk if this is your problem but, check the nut on the right side of the crank... if its loose or off it could cause problems. i recently bought a complete bottom end from a guy for $100. he sold it because he was having the same problems and he thought it was the timing chain or the valves. he pulled the side right side cover off and the nut on the crank that holds the gear for the timing chain came off, the gear slid over onto the threads for the crank and ruined them. like i said idk if this is your problem but its a possiblity. something to look into so you dont ruin a crank or worse...

This past weekend I installed a full HMF exhaust (thanks Armstrong87), k&n with outerwear - removed snorkel (lid on) and installed DynoJet kit.

DJ 165 main
3rd clip on the needle
stock pilot and about 2.5 turns on the screw ( i used the sound of the exhaust method)
Just about sea level.

I also tried a new gas cap - the old one had some rust on the underside, could have been clogged.
I am not sure what the tick sound is yet but I'm bringing it in for service in about a week to check that out.

My theory is that I was having some Pilot jet issues or the Gas Cap was creating a vacuum not letting gas into the carb.
It would normally die on me if I was engine breaking at higher speeds or when I would let off and blip the throttle - it would stall out while rolling (clutch in). From my research and reading, I learned that it is the Pilot and Fuel Screw that affect those conditions at low to no throttle.

One piece of advice I can offer is to really clean out the pilot jet and the three small holes in the throttle body. Mine had some nice brown goo that came out after a lot of spraying through the pilot jet. Previous owner did not do any maintance on the carb and it was full of varnish in the float bowl upon inspection.

It seems to run great now with the upgrades and I am still developing the right jet/screw/needle tuning for my machine.
I will keep this thread updated as I progress. My next idea is to bump up the pilot -


Thanks for the input guys.

I noticed that after I put a brand new stock NGK plug in, the ground electrode developed a really white glaze on it after doing some pulls for jetting. I wiped it off and am going to try it some more.
The top of the threads is black so I think I'm on the rich side. The insulator and center electrode still look clean.

Is the white color on the ground electrode a heat issue?

the insulation is what you are supposed to be looking at when you determine the jetting. some are going to jump in here and say you cant determine how your jetting is real well anymore with the chitty gas they are selling now and they are right. but if you do it right you can get an idea. the black on the threads is carbon. if the insulator is white then you are lean. it should be a cardboard brown color

Well I finally have all the kinks worked out and she is runnin purdy!

The intention was to buy something cheap, ride it until it died and that's it.
It has gone through quite the transformation since I purchased it 3 months ago, like save a stray.


Replaced front and rear bearings, added front right inner wheel spacer (previous ownder didn't think it needed one?)
New steering stem bushing
Replaced all waterpump internals to fix leak
Replaced Radiator (leaking)
Replaced Gas Cap
Upgraded to '06 front shocks
Added rear fender brackets and battery tie down
Upgraded to HMF full exhaust
Dynojet kit
K&N with Outerwears
Replaced Cam Chain with 3/4 DID
Shimmed Valves
Grips
Replaced Front Brake lever/master
Brake Light
Grab Bar
Painted A-Arms
added all misc. missing bolts/nuts



Still has 14/40 sprockets and I find myself hitting the rev limiter very fast in 1st-3rd. I think a new CDI is next.

So I just wanted to thanks the site and all the guys here - learned a lot in a short period of time.

i had the same problem with my quad after i got it dynoed, it was the float bowl height. It would cut out and die in higher gears. Check the height, it is not getting enough fuel.

Im sure the float bowl/carb are all okay...not having any fuel problems anymore. It just hits the stock rev limiter really fast now.
Not really a problem in the trails, only when I open it up on the straights.

Just shifting a lot faster now!