400ex run half throttle only

[ww228king]

well, i just got this 400ex, ran great for about a day and a half. then it started bogging out from half to full throttle... pulled the plug from the bowl and drained, it ran good for about 10 mins...
Then i took the carb off and clean the jets and cleaned the air filter and started it up and let it warm for about 3 mins... still half way throttle bogging....but sometimes it will buck at full throttle , like if the rev limiter was kicking in way too early. The pilot jet is #38 and the main is #150 and needle is set at 3rd from top, whites air filter , t4 exaust please help thanks

is the choke on??? if the chokes on it wont go past half throttle then itll start to bogg

does it have gas? is the gas on ON?

[REF426]

Sounds like old dirty gas to me. Check filter in gas tank. Was petcock on reserve when it started acting up? If you havent replaced gas then I would do that .

[ww228king]

choke was off, clean gas, but i didnt know about the filter inside tank. I will check that out next. thanks

[rooster_20]

The same thing happened to me a while ago and the place that holds the needle had worked lose and didnt pull the throttle all the way open sounds exactly like what you are describing.

[ww228king]

well, this afternoon i checked the screen in the tank , nuthing much there. I was just messing around and pulled the lid off the airbox and nuthing much changed. So then i unhooked the tube from the back of the carb to see if i could see gas in the carb. When i gunned the throttle with the tube off, it ran great. So mabe i am getting to much fuel. it has #150 for the main jet and the needle is set on the 3rd from the top. I also have another question ....on my main jet it has a jam nut that you can adjust up and down to pull the main jet in or out .....where should that be set....right now it is about 5 threads from the top. should i just screw the main jet in without the nut or adjust the nut all the way up so the main jet goes in farther?

[pit/wood]

check your float level,Its easy to bump your float and raise the fuel level in the carb too far.

[ww228king]

i dont know what you mean about float level....i didnt know you could adjust your level.......

well, so far i just cant figure it out ....i have lowered my needle, and put it back .....it really doesnt cut completely out...it just acts like the rev limit is kicking in way too early....i can go from say like 1st to third or something and go full throttle fine....but when the rpms get up just a lil bit, it starts to rev up and down real slow....and it was doing so good before it happened ...any help ?

[ww228king]

another thing that i dont understand is why it run good when i take the tube off.....i mean i take the filter lid off and no change then i take the filter off and no change , but he i take the tube from the carb ...it runs great...what does that have to do with the reving up and down

[parts eeter]

One thing is for sure.The problem is in the carb.Sounds like the float level is off or the float seat is dirty and doesnt stop the fuel from coming in past full bogging the engine.When an engine does this fire it up and turn off the fuel knob and it should progressively get better ubtil perfect and then it will run out of fuel.this is a sure sign that the float assy isnt working properly.Remove carb then floats and swab the float seat with a q tip. until it shows a clean swap.reinstall carb and ride.Have fun.Get a manual or have somebody scan the pages you need and email them to ya. You need to get your service manual to provide these details.If all else fails get a new carb from ebay.I know a guy who is parting new 05 models and I bought alot of stuff from him.He rox.

[Rip_Tear]

Is your air filter clean?

[jaysun]

Wow this is weird I'm currenlty having the same problem with my 400ex. I had the cam and rockers replaced, and now I'm having the exact same running problems you are describing. I have a new plug cleaned the air box. If I really run it hard it does better, but when up shifting it boggs like the choke is on. I will watch this post for what you find out.

[ww228king]

i guess i will look at the float tomarrow....dont know what to look for ... i looked at it before but seems to work fine to me ....how do you take it out....it has a pin it that wont move so anyway....i will check it out thanks

[m1ke]

Could the float be getting stuck?

[98warriorboy]

that sounds farmiliar cuz my brothers blaster done the same thing and what was wrong with it was that their was a safety switch on the clutch and it done the same thing ur talkin about! u might wanna check that out!

[ww228king]

well i will try to look at he float again....if i cant fix it , i guess i will just buy another ....let you guys know what happens....thanks

[ww228king]

ok i have done the test with turning the gas off and holding the throttle wide open, and it clears up when the gas starts to run out.....i have took the carb apart over and over and over and still cant seem to find the problem.....the float is fine ....it goes up and down fine....why is it messing up when it goes full throttle.....and another thing ...i dont see the gas coming ou tof the over flow hose....so i just dont get it .....please help me ....i am about to thrash this thing

[ww228king]

could it be valves or timing......i have cleaned and cleaned and no change.....and the float has no adjustment on it ...nuthng to bend...just plastic

[ww228king]

what does the black plastic piece that they call the air cut valve do? it has the hose comming off of it going over the top of the carb......i cant blow air through it...

[ww228king]

well, got the problem fixed.....turns out , it wasn;t the carb at all....the dang timing jump one tooth...so if you have the problem that i had......well, just reset timing.., but thanks for all thr replys