99 wr400f help please

Ive been pulling my hair out trying to figure out my wr400s problem it kicks over first kick sounds wonderful then 2 mins later its dead either idle or if i just putt down the street ive asked all kinds of questions in the jetting forum and done everything i can think of its time i ask for some help in person! I live in the san diego area and i could REALLY use a little help i dont have the cash to give it to the dealership to help me out but i would be so greatful if someone could help me. Thank you so much in advance


Sounds like fuel starvation. Check the fuel cap vent, float level/float sticking, petcock for good flow.

Sounds like fuel starvation. Check the fuel cap vent, float level/float sticking, petcock for good flow.

+ 1... That sounds like a fuel cap vent plugged.

good advise guys, that is how my yz400f ran when the gas cap stopped venting... unscrew it about a half a turn and try it, that is how i had to ride mine back to the truck that day.

a new cap fixed mine

lemme try that and get back to you all i took the straw off and tried but let me try the cap, if that doesnt work any other thoughts??? thanks guys


Well i just tried it and no go same issue still and it seems like it wants to backfire even more ??? Im so stumped !

well rats... hoped it would be that easy.. did you check pet cock for good flow ? When does it backfire, on decel ? Have you owned the bike awhile and ran ok before at your altitude, or any changes to the bike ?

How good should the flow be like full bore out the hole when i dissconnect the line from the carb and let it drain into a gas can? No changes at all nothing new except it doesnt work!! haha.... Also should the idle adjust be immediate? When i adjust the idle it takes like 20 seconds for it to change and when it does its VERY different! It also now seems to be idling a little irratic! One more thing im not sure if it will help but it is on reserve would that effect anything??? Sorry for all these questions but im desperate!

Whoops one more answer yes deceleration! could the air jets be clogged? I didnt really mess with those!?

backfiring is caused by a lean condition... probably because the bike is starved for fuel... pull the fuel line from the carb and check the flow from the fuel line, it should be a good steady flow..

I have a feeling either your float is stuck, you have something in your float valve orifice or there is a clogged jet in the carb.

If the pet cock and fuel line are delivering a good flow of fuel, I would remove the carb... layout a clean shop towel on the bench and disassemble, cleaning everything everything as you go.

Has the bike and gas been sitting a while?

not sure dude... I would look at the pilot jet, pilot circuit on the carb. i had mine out a couple of times and never got it clean. the early fcr's are very touchy. decel pop can also come from air leaks. check carb boots and exhaust connections. The fuel should flow pretty good, the reserve should not matter, but when you have the hose off check the flow on both on and reserve. My guess would be in the pilot circuit.

boy I can't thank you guys enough, I just took the carb apart again and it has all new jets in it (pilot and main at least) I checked the accel pump it's seeeems ok kinda old looking 1.7 ish turns out on fuel air cleaned the air jets(?) and I'm going to look in my book what the pilot circut is and get back to you man have I learned a lot! This is my first delv into carbs! Keep it comming guys this is so great I can't thank you enough!

I just took off the bottom of the carb again and I think there is something jammed in re main fuel line how would you guys purpose I get it out of there I've tried everything any tips!

post a pix of it ???

I think I'd have to have a snake cam!:thumbsup: I was wondering how unrestricted should the flow be? It's hard to even blow through, also can you remove the line where it attaches to the carb?? Thanks again everyone!

Yes, you can remove the fuel line from the carb fitting. I think the swivel is pressed into the body though and I am not sure if you can remove it or not. Can you describe what you think is stuck in there and where it is stuck with a little more detail?


I honestly think a bit of one of the qtips i was using got stuck in there and its jammed just after the 90 bend carb side! I tried an air compressor and it didn't do it even a piece of springy metal rod and nothing i cant even blow air through the pipe (blowing from where the fuel line would be attached and put my finger over where the fuel float valve screen would be and its almost zilch! im guessing it should flow pretty damn well! Thanks guys YET again for all this help i cant express it enough!


If it is stuck in the carb inlet, then remove the needle and seat and blow air in reverse. If you blow from the bowl side it should come loose and blow out. I wouldn't recommend using the Q-tips any more for carb cleaning though. Hope this helps.


I dont think i will use qtips anymore!!! Darn thing caused me A LOT of grief. im gonna try that tonight, Whats the best method for cleaning your carb. Thanks again guys!


Depends on how dirty and what kind of dirty it is. If you are just doing routine cleaning then I would suggest the spray carb cleaners and if you have to use any tools then a small brass brush or even an acid brush will work. But basically if you remove all of the jets and clean them with the spray cleaner, make sure they are clear and you should be good to go. If it is really gummed up from bad gas or something like that then you can take the bowl off, and soak the whole carb in a can full of cleaner overnight and then rinse it with the spray cleaner. Finish it off with some compressed air and you should be good to go. Hope this helps.


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