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Thread: 400ex wont run without choke

  1. #1
    Join Date
    Feb 2010
    Posts
    1

    400ex wont run without choke

    I bought a brand new 2007 honda 400ex recently. I have ridden it about 4 times. The first three times it ran perfect. The next time it didnt. It wont idle without the choke being on even after being warmed up and it wont run properly unless the choke is fully on. If I put it at half choke then it runs and idles fine at half throttle but if I go full throttle it bogs down and almost dies. It ran fine one day then the next this happened. I have no idea what it could be.

  2. #2
    Join Date
    Jan 2004
    Location
    south central oklahoma
    Posts
    2,654
    main jet could of fell out. Just a guess. Then again my buddies 400ex would idle just fine when that happend. I would clean the carb and airfilter really good. Being new I don't see this being the problem but give it a shot
    2006 300EX web cam, wiesco 11:1 piston, shorty cobra pipe,dynojet jet kit,GDH oil cooler,K&N filter with outerwears filter & airbox cover,CRJ 1 1/2 front wheel spacers,21" front,18" rear fast trekkers all around on T-9 pro series wheels,maier front and rear plastic, Pro Taper SE atv-mid handlebars,DG fat series grab bar,DG front alloy bumper,burgard +2+1 a arms, Diamond J Customs Shock Relocater with 450R shocks, G-force Axle,Raptor Shock

    2000 KX250 Uni Filter, FMF shorty Silencer,FMF Fatty

  3. #3
    Join Date
    Aug 2006
    Location
    wv
    Posts
    96
    did you was it and get the filter wet?
    is your gas tank vent hose plugged?

  4. #4
    Join Date
    Mar 2010
    Location
    Findlay, ohio
    Posts
    26

    Re: 400ex wont run without choke

    i would try cleaning the carb... mine did the same thing... while you got the carb apart go with a 42 pilot jet... it will help so much on starting wont ever need the choke... if you have a slip on you need to atleast go with a 155 main jet to or you will burn your vavle seals up because they come stock running lean out of the factory... but clean the carb and air filter im guesing thats your problem
    440ex/with JE 12.1 piston/old syle stage2 cam hot cam/port&polish ported head/hotrods crank/2degree timing key/no base gasket for beter deck height/k&n filter with flow kit/fmf power core4 shorty cut down 4in./powerbomb header/dynojet kit MJ185 pilot jet45/ 1/4inch intake spacer/ choke removed/16T 36T sprockets/dougless polished rims 22/6/10 fronts/ 20/10/9 rear holeshots/ tripple rate works front shocks

    build on the cheap
    2003 banshee.. 60 over wiseco pro lite pistons, FMF fatty pips and silencers, boost bottle, boysen reed pettles, K&N filter, vitto key, jetted stock carbs, plus2 durablue axle, 1.5 spacer for the front.. i have 35 mill keihin D slid carbs not installed yet... and soon to be head milled... i have 675 dollars invested into it!!! including the bike!!!

  5. #5
    Join Date
    Feb 2009
    Posts
    157
    It shouldnt be dirty, you said it was brand new, right? The first thing that came to mind was something is clogged in the card, but that shouldnt be the case. Take it back to the dealer have them fix it. Should be under warranty if its new.
    -04 DVX 400, +2 FULL FLIGHT FRONT A-ARM, LTR450 front shocks, +1+3 G-force rear axle, +1.25 ATV Four Play rear swingarm, FMF T4 exhaust, K&N powerlid, Twin Air filter setup, K&N powerlid, 400ex air boot w/ custom airbox inlet, YFZ FCR39, HotCams stage 1, DRZe Kit, RevMax CDI, Pro Armour Tether, Pro Armour Nerf Bars, Maier Roost/Handguards, Armadillo swinger skid, Rear E-brake block off plate, Mod Quad Case Saver, Razr rear tires

    -HYBRID 350X IN A 250X FRAME, trx250r rear swingarm and suspension, Lonestar 2+2 rear axle and 6 gears of fun. thinking about selling

    -86 LT250r All stock, My piston shattered
    parting out if you need anything

    -2001 Foreman 450ES

  6. #6
    Join Date
    Nov 2009
    Location
    vegas
    Posts
    844
    dont know the carb u are working on but i have had the clip on the needle come off and cause the same condition on my old 250rs just an idea

  7. #7
    Join Date
    Mar 2010
    Location
    valdez, alaska but im from miami
    Posts
    4
    hey 440exhonda man u said something about the valve seals burnin up if u dnt jet it with an aftermarket exhaust. wel i removed the silencer on the stock exhaust would that effect my engine?
    Honda for life!!!

  8. #8
    Join Date
    Mar 2010
    Location
    Findlay, ohio
    Posts
    26
    if you put a aftermarket slip on exhuast and dont jet it to atleast a 155 main jet then after a while it will burn your exhaust side valve seals up... i did it to mine... the seals are cheap its just the part of doing it cuz its a pain.. but bump your main jet up to a 155 or 160 even for a lil more power and to be safe on your vavle seals... they start so much easier to if you put a 42 pilot jet in also.... i would clean the carb you said its an 07 so theres a chance the gas has had been sittin in it and gummed up your carb....
    440ex/with JE 12.1 piston/old syle stage2 cam hot cam/port&polish ported head/hotrods crank/2degree timing key/no base gasket for beter deck height/k&n filter with flow kit/fmf power core4 shorty cut down 4in./powerbomb header/dynojet kit MJ185 pilot jet45/ 1/4inch intake spacer/ choke removed/16T 36T sprockets/dougless polished rims 22/6/10 fronts/ 20/10/9 rear holeshots/ tripple rate works front shocks

    build on the cheap
    2003 banshee.. 60 over wiseco pro lite pistons, FMF fatty pips and silencers, boost bottle, boysen reed pettles, K&N filter, vitto key, jetted stock carbs, plus2 durablue axle, 1.5 spacer for the front.. i have 35 mill keihin D slid carbs not installed yet... and soon to be head milled... i have 675 dollars invested into it!!! including the bike!!!

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