400ex wont rev up

[commandman10]

Hi, I have an 02 400ex with HMF pipe, drilled airbox and jetted carb. It starts fine and idles good. It revs good til about halfway where it just wont go. It doesnt bog or hesitate but will simply not rev past that point. I can hold the throttle wide open and not hit rev limiter. Filter is fine, there wasnt any junk in the floatbowl but I didnt clean the carb out. The plug was black and sooty. Happened wile quad was on jacks having a new carrier put in. Thanks

Edit 12/16- I forgot to mention this problem apperaed after the quad sat for 2 weeks while I put a new carrier in. If that helps at all.

[F-16Guy]

Check to make sure you didn't pinch any of the carburetor vent lines that run down to the bottom of the frame near the swingarm mount.

[commandman10]

Would that do it? I bet I did putting the jack underneath the engine skidplate to pull off the tires. Il check when I get home. Thanks

[commandman10]

No luck, what else should I try?

[sextonjd99]

Sounds like like the slide came loose in the carb. Pull the top cover off the carb and check to see if the plasitc piece that connects to the slide is still attached.

[commandman10]

Yah so no luck, only home to work on this thing once in a while. Could it be a coil or something?

[commandman10]

Edit 12/16- I forgot to mention this problem apperaed after the quad sat for 2 weeks while I put a new carrier in. If that helps at all.

[79400ex]

It sounds like the carb is dirty.

[oleboy87]

could it be jetted wrong and ya jsut didnt notice it till now?

[commandman10]

It ran perfect until I first fired up after the carrier work. I am never home but Im gonna go through the carb again when I get home, I halfassed it in an 1/2 hour last time.

[drew416ex]

Check where the airboot connects on the airbox side. It may have come off. Had the same problem and that was the cause

[f4istunna]

sounds like something in the carb? Check to see that its getting good spark to rule out electrical.

[AutoRoc]

Mine did this and then eventually wouldnt even fire.

Main jet was gummed up completely. As in I couldn't see light through it! By what? I have no clue. I strained the entire tank and found nothing bad.

[commandman10]

cleaned carb and no luck, gonna try and borrow a coil.

[F-16Guy]

Did you remove the main jet and verify that there is nothing in the passage? It takes something no larger than a grain of sand to completely block the main jet and cause what you're experiencing.

BTW -- If you're the class of 2011, the apostrophe goes before the 11.:devil:

[commandman10]

The main jet was unobstructed. Not gummed up or any sign of contamination. I questioned the pilot jet because it has a tiny hole in it but can anyone verify that is normal? I heard pilots have a very small opening and it was only visible when held up to light. I did not rule out dirt in the pilot but the opening seemed to be fine and if there was anything in it I prob blew it out.

[drew416ex]

Did you check the air boot like i mentioned before?

[limetimeracerII]

If you still haven't figured it out. A couple more suggestions. Water in the gas. Did you look at the gas in the bowl when you took it off to see if there was water in with the gas. It looks like little bubbles on the bottom of the bowl. If that isn't it check the timing. One time when I put my engine back together, I timed it with one of the marks that comes before the TDC mark. It did exactly what your describing. Now unless the timing has jumped or you have been in the engine before this happened, I doubt thats it.

[sn0wrider]

had the same problem... but it was the jetting that was fu cked up. It was fine at about 45degrees, but in 30 degree weather it wouldnt go past about half throttle. try a new jet n see if that works

[commandman10]

The airboots are good with no cracks or leaks, the jets and the carb are clean, I checked for water in the gas and it was good, I have not checked the timing or tried rejetting. Should I toss in a larger main jet possibly? I have not had anyone say whether or not the coil could be bad. Thanks a lot everyone

[fA_dAvE]

mine did the same thing awhile ago. i thought my jetting and crap was off after i installed the HMF pipe but my problem turned out to be the ground wire on the battery. check that, mine was not entirley broken but enough to cause a problem when it was rev'ed up

[sextonjd99]

Did you check that the slide in the carb. is moving when you give it throttle?

[commandman10]

the ground appears to be flawless and the slide moved freely and the butterfly opened correctly. I might have to have a shop check this. Im gonan try the new coil when I get it but am lost otherwise.

[01 416EX]

Hi, One more thing you can check is to make shure the parking brake lever by the clutch handle is not partally pulled away from the switches. Sometimes mine will stick and not return all the way and will do the same thing yours is doing.

[commandman10]

I can only see one switch on that perch and that is for the clutch. Am I just missing it? I tried another coil to no avail. Thanks

[exracer416]

i know this is a reall old post. but im wondering if you found a solution?