KFX 400 Dies when throttle touched only will idle with choke

9 replies to this topic
  • Kfxrider90

Posted January 22, 2011 - 05:26 PM


06 kfx 440
Jetted perfectly on stock 06 carb
Big Gun CDI Rev Box
LRD Full Exhaust
Has about 200 hrs on this setup.
Oil changed regularly.
Has a fresh oil change with 10 min of idling on it. (come to think of it before changing it it seemed to die after a few min of idling to warm up, but I thought nothing of it and changed the oil.)

Sat for 2 months without being ridden, but ran perfectly when parked originally about a week before the oil change. Went to pismo and it would not run after a 9 hour drive to the dunes . Spent the weekend trying to fix things with no improvement. Before I left the bike ran sluggish, but ran enough to load it.(MISTAKE) #1 Needed choke though.

The bike will turn on and idle normally with choke on about 1/2- full choke for about 3-4 min then die on its own, but the second I even touch the throttle even a hair it instantly dies. No matter if on prime, reserve or on.

91 octane gas is still old and I did not use sta-bil. Wouldn't it not even start if the gas was totally horrible?

What I've done so far

-Cleaned the main jet and pilot jet with carb cleaner. You can see daylight through the holes. Even before cleaning everything looked new. Float did not seem stuck at all.
-Unplugged CDI and plugged back in
-Grounds are on tight.
-The little wire near the throttle is plugged in (not sure what it is even)
-All hoses are attached to the carb. Including the air box and hose from intake port to carb.
-I blew air through the petcock tube into the tank using the healthy choice of using my lungs. Gas flow didn't seem like a river coming out of tube, but about a stream.
-Even tried starting with gas cap off. No difference.

What do you think I can do? I'm so lost and frustrated. I've had 0 problems with this quad until now.
My k&N filter seems a bit dirty though, but I don't think its enough to make it not run.

  • onespeedonly

Posted January 24, 2011 - 02:06 PM


Basically same problem going on at my property right now. My 06 Kfx 400 is all stock though. Starts right up every time idles perfect ..... soon as you give it gas it will respond a little then quickly die. If i cant figure something out, I'm gonna have to scratch the shit out of my truck to get it lol. Has ran perfect till this point very low hours. Any ideas?

Also I see that his quad runs and idles with choke..... my is the opposite. If i pull the choke down it dies.

  • zimak

Posted January 24, 2011 - 03:31 PM


VERY common and easy to fix issue.

I cant tell you how many times I've fixed this exact problem as our riding group mechanic.
Carb cleaner does not get the crap out of the jets the way you think it does.
1. Go buy a cheap set of guitar strings.
2. Cut them down to a managable length and add them to your tool box.
3. Pull those same jets out and wet them with carb cleaner and run the strings through the jets. Start with the smallest and work up to the largest that will fit through.
4. Put it together and ride on.

Never fails for me and the symptoms are exactly what I see and what goes away afterwards.

  • zimak

Posted January 24, 2011 - 03:33 PM


KFXrider 90:

Here is where things went wrong:

"Sat for 2 months without being ridden, but "

Save yourself the trouble and spend the $2-3 at home depot for some tubing and make a little jig to drain the bowl anytime the bike is going to sit.

  • Kfxrider90

Posted January 28, 2011 - 06:14 PM


Well I put the OEM CDI in and no difference. I then took off my gas tank to see if there is spark. There is a lot of spark with the OEM CDI and Big Gun CDI. The one thing I noticed was that my spark plug seemed very black. I'm going to purchase a new one since it is about 2 years old.

Any suggestions?

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  • onespeedonly

Posted January 29, 2011 - 07:43 PM


So removed carb and did thorough inspection. Found gigantic gas booger hiding in the main jet. Cleaned everything, set float and buttoned everything up. Runs like a champ. :thumbsup:

  • Kfxrider90

Posted February 05, 2011 - 08:50 PM



Today I cleaned the carb really good. I found some corrosion inside my carb, but it came off easy with cleaner. Took out all the jets and cleaned them as well as the needle and float. Basically if it can come off I took it off and cleaned it. I also cleaned the sparkplug and checked the gap (it was perfect) I also cleaned out the fuel filter.

So now atleast I can get it to start( last week it wouldnt even do that) for about 20-30 seconds even without choke which is a plus. The bike still instantly dies even with the ever so slightest touch of the throttle.

I'm lost help!!!

  • onespeedonly

Posted February 06, 2011 - 05:25 PM


Kfx rider did you set your float and make sure all the passages in carb are free flowing.

  • Kfxrider90

Posted February 07, 2011 - 02:27 PM


Yes I did.three times now taking the entire thing apart. Weird thing is using the tiniest amount of startting fluid it would run and the throttle would work for about 10 seconds.

  • Kfxrider90

Posted February 12, 2011 - 04:04 PM


OK new UPDATE 2/12/11

Got a used carb and installed it it started for a second and thats it.

So i did a compression check (cold) and I got 95lbs....yikes!!! I then decided to check my valve clearance(while cold) and I couldn't even get a .08 feeler gauge under the intake or exhaust. I'm not sure how much of a difference if it was warm it would make.

BTW- i didn't find any metal flakes or anything.


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