WR400F 1/8-1/4 Throttle miss/stumble/"out of fuel" feeling

29 replies to this topic
  • Brrrap Brrraaaap

Posted October 30, 2015 - 03:45 AM


So bought my first bike put a set of allterain tyeres on only to find its real crap in the 80-100 kph range coasting along at 1/8-1/4 gas its like you running outa fule and need to flick the fuel tap but you close ore open the throttle just a bit and its fine its so frustrating


a bit about the bike

starts grate no choke just one twist on the throttle and a good kick usaly first kick if not garinteed on the second kick hot or cold

16/50 sprockets on 21/18 im looking for a set of super moto 17 fims over size front brake and all that so i can have dirt wheels and road wheels

the bike is really crips it loves to stand up 2nd or 3rd with out trying pulls strong evan in 5th to the limmitter at 155-160

stock exhaust and air box


striped the carb today and replaced the head to carb rubber boot was showing its age few cracks i was thinking it may have been sucking air under the light throttle and messing it up but not the case i also checked the hot start nope its tighter than a ducks ass same for the relating vac lines


i was suprised how cleen it was only mankey bit was the top of the slide was all black nasty


i did notice where the slide rollers spend most of there time its worn a chanle into the carb body you can feel it when the slide rolls up and down also theres a little shake to the slide as in movement in the direstion of air flow if the makes sence also where the two red rollers go in that little top bit of the slide theres a bit of slop its not huge but i donno whats normal or exceptible im just thinking maby the slide is rattleing around or jumping giveing that miss/out of fule feeling when coasting 80-100 4th or 5th it dose happen at slower speeds but i can shift gears to get rid of it


needle is OBDXM middle clip

the needle thats ajustible from under the carb bowl is 2 1/2 out what ever its called

168 main

45 pilot

62 start

75 pilot air

200 main air


i was reading up a bit and found the TPS to be the sorce of some guys woes so at the time i checked mine and it was in speck for that the book said but this is with it off the carb so will re check it when back on the bike also i think theres some way to adjust it or some thing that the book dose not say?


also i did have the regulator go bad and i was getting upto 35-40V AC going threw everything when the bike was reved maby its dammaged the CDI or TPS? ive now got a new reg and its back to 12v or close enugh


anothor thought was the bypass valve thing that "Ts" off the head to the hot start the diafram thing with 3 hoses what ever its called i dont hae the book in front of me could that thing be opening and closeing causeing this miss thing i was looking at it and it seems the function is to lean the mixture under high vacume


ive not tyred the tps un pluged and i dont really want to run it that way i like how the bike responds and trys jump out from under you dont wann lose that


also a freind has the same bike altho he has a pipe and his carb has been tweeked by someone maby not in the correct way anyway his bike dosent do this miss/surgeing thing so besides swapping a bunch of stuff back n forth


his bike is lazy tho its not responsive like mine and its slower i can out run him it needs some work it pops and back fires when you let up think he needs valeves or something done


i like mine better but the miss/surge is CRAP why mine and not his?



  • RiderDeAzul

Posted October 30, 2015 - 05:19 AM


Play around with your fuel screw, there is a sticky about that. You might need to go up a pilot jet size too.

  • bourneaussie

Posted October 30, 2015 - 06:43 AM


Youre way overthinking this. Its going to be a carb set up issue. Reqd the stickys above.

Also your mates bike which you said is popping on decel, is running lean

  • bobpara

Posted October 30, 2015 - 09:52 AM


Before you go too fat with a jetting issue, consider this:


I have a 06 WR450F and oddly enough it is  a carb with a TPS (throttle position Sensor). I'm not entirely sure why they designed it this way but on a wide open road (80 -100 kph) = 50-60 mph


I had a post earlier and I think I titled it "WOT Stumble'


Kahranee who trolls this site alot pointed it out. The TPS gets confused at WOT between steady state running and Idle....its an ignition related thing. it  toggles between two modes and hence the stubble that feels just like you are about to run out of gas.....but it keeps running


I bought an aftermarket ingition module for $350 or so and it took 75% of the problem away


I think you can verify if this is the problem by disconnecting the TPS and take it out for a balst and see of it goes away


The TPS is a black plastic blob on the L side of the bile and a 3 prong grey colored connector comes off it it about 6" away on the same side


....try it

  • Brrrap Brrraaaap

Posted October 30, 2015 - 01:28 PM


ok guys first i need to sort the throttle cables one i frayed bad like 4 strands holding it a local guy aparntly re dose the inner with ends and such for cheep so long as the outer is good


ill give that tps a go un pluged but i think first i should check its set correctly im off to find that post i read some thing about needing the tps on the carb and it needing to be set for idle speed


so you guys think i shouldnt worry about the carb being a little worn or that air valve vacume diafram thing near the choke (not hot start) i wish i could hae taken pics of the slide and body


a buddys old man has a big bag of jets from all sorts of things ill see if he has a larger pilot (thats the fule one right?) that affects the # turns on the screw under the bowl?


im not really wanting to jet the bike i think its ok where it is it feels fun to ride and keeps you awake


bikes also gotten me in truble since putting it on the road so ill be haveing a forced brake from rideing and driveing.. road rules suck they need more free or near free places to go fool around that dont require you to modify your bike if you could simply go half to an hour to a place that let you roll in with just a helmet sine the paopr and ride to get it outa your system i tryed a place nearest to me 2 hours thats cost like 50 bucks a day got told i need frame sliders axle sliders barb buster no coolant only water oil breathers into catch tank sump plug tie wired bla bla crap crap 90% of people say &%$#@! that thats cash and time ill just ride the street




off to pull the cables and hopefully get em fixed up like new

  • RiderDeAzul

Posted October 30, 2015 - 08:45 PM


The pilot jet is only active from idle up to 1/4 throttle (correct me if I'm wrong someone) and the air/fuel screw you turn in for a leaner setting and out for a richer setting, try turning it out as far as you can without the bike stalling and if you turn it 3 times or more out without it stalling, you need to go up a pilot jet. And you can tell if your hot start plunger is having issues because it will backfire like hell, my brother's bike had that issue when he picked it up

  • Brrrap Brrraaaap

Posted October 31, 2015 - 02:31 AM


Rider: ill have a go at that tomorow


Bournaussie: ill check the stickys out and get back


Bobpara: i think your right man i un plugged the TPS and its mostly gone only the slightest hint remains now BUT its still there when i slowly twist the throttle open from a standing start threw the gears the same "running outa fuel but keeps going" feeling so that tells me from (my limeted knowlage) that its also part carb setup i did go back and turn the air/fuel screw (one under the bowl) all the way in and back out 1 1/4 turns what my factoy book says and that made the bike more snappy like it was with the tps connected as it lost that snappyness when i disconectted it


Rider: i think your onto it as above this "outa fuel feeling" is only pressent in the 1/8-1/4 throttle range when at steady speed 80-100kph or when just slowly rolling a small bit of throttle in off the line


i did test the tps again when on the carb 4.34K ohms (blue + and black-) also 0.68Kohms closed 4K ohms wide open (yello + black -) that restance changes nice and steady no jumps or spikes so it seem the tps is ok by the book i have altho i thiught there was some thing about haveing the bike running and back probeing it to test it correctly in some sticky some place


im off to read the forum


ohh the old girl and some maitainance parts grips when all sticky after i went to the car wash throttle cable nearly in two head to carb boot cracked but not yet threw to inside messed around with the cable bracket to get them not to rub the steel nut






  • Krannie McKranface

Posted November 01, 2015 - 11:40 AM


You need to replace your needle jet, it is worn out. That's why you get an 'on the needle gurgle'.

Your needle jet (not the jet needle) has ovaled, and is no longer sealing properly around the needle.

While you are in there, replace the slide plate, plate seal, set your float height, and check all your harness connections.

A bad ground makes the TPS problem worse.


Unplugging the TPS will help the problem, but worsen the throttle response.




  • Brrrap Brrraaaap

Posted November 04, 2015 - 05:48 PM



i never thought to replace the needle jet tube wouldn't the oval just let more fuel out everywhere in the rpm?

what is this on the needle gurgle?


i just gave the slide plate a slight rub on 1200 wet n dry on sheet glass


thats a different carb to mine the float is different few other bit as well


ive been thinking about installing a wide band O2 sensor and gauge on the bike to see what the fueling is doing but keep talking my self outa it

ive installed a small 12v battery and rectifier on the bike for the head light, tail/brake light, indercators and horn i isolated the grounds for them so the battery is seprate from the bikes negative/ground this make it not so sketchy if you stall pulling out of an intersection at night or just plain waiting for the lights to change its hard to be seen wit dim lights at night while not moveing the battery fixes this anyways back on point..


i think if i did get the wide band O2 on there id see something nasty and freak out but it would give me a chance to tune the carb settings with more than the seat of your pants method


one thing that may confuse things is the CDI changing timeing tables that can affect ARF as the burn may or may not be compleat before the gasses get to the wide band


ill see to a carb kit or maby a new carb altogether? ive not seen or know how much ware is normal or exceptible but im sure my carb is well worn where the slide moves the whells have cut the carb body and there is groves where the wheels spend most of there time i was moveing the slide by hand after i cleaned it all and its deep enugh to feel the slide hit that bit then jump over it

is it possible the slide is simply bouncing around in a fashion that would equal you rapidly twisting the throttle open closed slightly ?

  • Krannie McKranface

Posted November 04, 2015 - 05:56 PM


You are over and under thinking this


Sanding down the slide plate will make it seal worse.  You  need a fresh slide plate seal.


The needle jet wears out in 100 hours or so depending on how you ride.

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  • Brrrap Brrraaaap

Posted November 04, 2015 - 06:33 PM


just looked at carb parts holly crap they must be gold plated the slide plate thing 160 bucks that thin bit that has the ruber ring on the slider assembly 615 bucks what the hell do they think anyone will actuialy pay that




haha 700 bucks for a stock exhaust yeah right   https://www.thumpert...999&model=28985

  • Brrrap Brrraaaap

Posted November 04, 2015 - 06:35 PM


ok ill see to getting a new needle jet tube and slide cover plate with rubber sealing ring

  • Krannie McKranface

Posted November 04, 2015 - 07:22 PM


Look around price wise

BikeBandit is usually good

CRF's only is really cheap


The slide plate seal is the same across all brands, honda, yam, kaw, suz, ktm, so you can search all for the best price.

  • Brrrap Brrraaaap

Posted November 05, 2015 - 01:05 AM


well ive been using the bike a fair bit put about 15 hours/1200kms on it decided i should change the oil after all ive not done it since i bought it


whats normal to see? im assuming this is a bad thing..






i used a clean pan to drop the oil from the tank and case into it looked fairly good the tank screan was clean


can you buy magnetic drain bolts for this bike?


anyways looks like ill be disqulafyed from driveing/rideing for a while so the bike may get a tear down for a look see what do you guys think?

  • RiderDeAzul

Posted November 05, 2015 - 04:30 AM


Well, unless you put glitter in your oil that is not a good thing. I would take your head and cylinder off and check both for excessive wear/gouges, if you don't see anything there it's your clutch area or transmission most likely. But, I tend to overdo most anything on my bikes and quads.

Edited by RiderDeAzul, November 05, 2015 - 06:41 AM.

  • Brrrap Brrraaaap

Posted November 05, 2015 - 05:51 PM


sadly i dont think its from my clutch as i took a look as it seemed the easyest thing to check first


look like a new clutch to me there is little marks where the parts drive on each other but nothing that can be felt with a finger nail or small pick also the frictions mesure like 0.05mm from the top limit in the book so heaps of meat on them


i did notice the thing was really dry ?? thought this thing was meant to have a bunch of oil over it to cool it? also i dont know if the steels are supost to have what looks like heat discoloration?


pictures over on the other post


rather than have two posts on the same thing (satrted the other as i think it should be a seprate thing) ill stop posting here and go to the other one http://www.thumperta...ying-used-bike/

  • Brrrap Brrraaaap

Posted November 06, 2015 - 01:32 AM


droped the oil again looks nasty so im callin it no more rideing time to pull her down and see whats going on disapointing really it rides well but better to pull it now vs contunue to ride it and put the rod out the case or something silly

  • RiderDeAzul

Posted November 09, 2015 - 06:12 AM


sadly i dont think its from my clutch as i took a look as it seemed the easyest thing to check first


look like a new clutch to me there is little marks where the parts drive on each other but nothing that can be felt with a finger nail or small pick also the frictions mesure like 0.05mm from the top limit in the book so heaps of meat on them


i did notice the thing was really dry ?? thought this thing was meant to have a bunch of oil over it to cool it? also i dont know if the steels are supost to have what looks like heat discoloration?


pictures over on the other post


rather than have two posts on the same thing (satrted the other as i think it should be a seprate thing) ill stop posting here and go to the other one http://www.thumperta...ying-used-bike/

If you drained the oil prior to checking the clutch, it is normal for it to not have oil all over it, atleast mine never does.

  • Thommo_400f

Posted November 16, 2015 - 01:21 AM


I vote 100% it is s worn needle jet. I had exactly same problem. Just took me about a month to find it !!

  • RiderDeAzul

Posted November 17, 2015 - 08:12 AM


Did you ever find the needle, and if so, did it fix your problem, my bike acts normal everywhere except in 5th gear 1/8 to 1/4 throttle, I am wondering if this could be my issue as well.


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