01 ex barely running at 1/8 throttle?

[ddw350]

hello,im new here..but old hat at 3wheeler world!...anyhow i purchased my nephews 01 400ex as he needed cash bad.it has a dg slip on,and somekind of aluminum airbox with no lid,and a unifilter.problem is,right off idle to almost 1/4 throttle it hardly runs,pops gurgles,sputters..anything over that it runs great,ive tried simple adjustments,i have NO clue what the factory jetting is supposed to be on this,nor do i remember what jetting is in the carb now,projects been on hold for 4 months now so i forgot ,carb is super clean..actually the whole bike is,he put a ton of stuff on it then it sat in my parents barn.. plug looks decent and altitude is like 450 feet or so..thanks for any input

[cam19aro86]

Sounds like a jetting problem. After a slip on and a new high flow air filter (especially with no lid) rejetting is a must. You probably need to go down a clip on your needle to make it a little fatter. There is a very good article on jetting on this site under ARTICLES. I would say to go to that and read up a little.

[BERT306]

Idle to 1/4 throttle would be in your fuel screw setting and pilot jet.

easiest fix would be to back OUT your fuel screw until it idles better. If its over 3 or more turns out u should put in a bigger pilot jet. I believe the fuel screw on a 400ex carb is under the carb in front of the bowl. Most likely a PITA to get to.



Hope this helps

[cam19aro86]

Yep my mistake, don't move your needle.

[ddw350]

i figured jetting,like i say,i have no clue what the jetting is factory,who knows whos been inside there boogering around,the idle is ok,its right off idle is when it acts up,i made a lid for the air box and it literally wouldnt move,like the choke was on..yes the screw is a pain in the a#@ to get to,i made a custom driver to get to it though,i tried to find the factory parts to put back on,i couldnt though.... i appreciate the help guys...

[ddw350]

i found some assorted pilots,hopefully i'll have 1 bigger when i see what one i need,i may put 2 sizes larger in if i have that one....

[DP400]

Stock Jetting is 38 pilot and 148 main, keihin jets. I just put a hmf slip-on on my 02 and lid on with a k@n. i'm in ny so our weather is colder now, 510 elev but, i ended up with stock pilot and 152 main, screw 2 3/4 turns out. i just got a 155 main i think that i'm going to put in for the rest of the winter. the only thing is that i'm getting poping on decel not to bad though. i tryed a 40 pilot jet and when it was running i had screw 1 turn out and there was back firing from the carb and when i took the carb back out it smelled like gas real bad. i'm not sure where my needle is though, never had it apart, i think it is stock, but i'm 3rd owner so who knows.

[ddw350]

UPDATE...

i installed a #42 pilot jet,airscrew out 2 3/4..and main jett is at 156?? sounds large,but runs great,so someone has been inside there already.... runs and revs up excellent! thanks guys