"coughing" at idle

[Honda6sv]

Heres the scoop..ive tried a few things but nothing is seeming to work.,..maybe someone a touch more experienced can help me out. Alright, First off its a 2003, 400ex of course...Ive got a fmf hi flo header with powercore 4 silencer. Also, I have a UNI air filter with and open aluminum air box. I bumped my main jet from the 148 to a 152...and bumped the pilot from a 38 to a 40. Both jet were cleaned to see if that helped...That didnt work. I turned the fuel mixture screw a couple different ways...nothing. On some carbs there is a "plug" that houses another mixture screw, is there any such thing on my carb? If so will that help me? Any info would help...If not...ill just buy an edlebrock...

[Sparky_20]

it sounds to me like your either getting too little fuel or too much air. Does it run any different on reserve? If it does then your fuel valve right there is probably clogged. Check the clamps on your intake hoses too to make sure they are all tight and not leaking any air. If neither of those works then I would bump up your main to 155-158 and get a 42 pilot jet and see if that helps.

Does it only run like crap at idle? If so then that means the "slow" circuit of the carb needs to be checked out. Check out this link, it explains in detal about the different circuits of your carb.
http://cdracingonline.com/id57.htm

Good luck!

[Honda6sv]

i know all that lol...all my lines are good...everything is in perfect order...It ran perfectly when i put in the new jets last summer...after awhile it started getting that cough to it.

[underpowered]

a cough at idle is a sign of being to lean, it is asking for more fuel. how many turns out is you air/fuel screw currently? i would try a 42 pilot jet and about 2 1/2 turns out on the a/f screw.

[jrafter]

maybe you have an air leak......silicone everything real good.

i had the same problem and this helped.

[400exrider707]

Bump the jets up like suggested.

[4 shizzle]

Why is the answer to every question on here, "its your jetting". How does the jetting all of the sudden go wrong? He doesn't even tell us whats wrong and "its the jetting". More info would be helpful to helping you. More than "cough".

[CDCHONDAS]

its very possible that another part of your idle circuit is plugged and the pilot is actually open, I assume you left it set the winter?, try to adjust the mixture screw first but I would think that if its in the carb, something is plugged, not just jetting, that is if it ran right before and nothing has changed, also the suggestion to silicone everything is silly, just spray some starting fluid on the carb boots, intake manifold and listen for the engine to rev up some, if it does- theres your leak.

[underpowered]

well by my asssumption a "cough" is like it is idleing and all the sudden it just coughs for lack of a better term. the motor just almost like stops running for a split second. it is becuase it is to lean, the cough is due to lack of fuel. it could be an air leak, but if it was it would do it everwhere, not jsut idle. so my guess is the pilot jet needs a bump. many run a 42 pilot on teh site, but for my application that was actually to lean, so when i had my stock carb i actually ran a 48 pilot. now with the FCR i run a 55 pilot. jetting, if not done correctly will really mess with a bike. and yes it can "go wrong" all the sudden. any temp changes, weather changes, elevation changes, fuel changes (even from winter blend to summer blend) and many other small things you don't even think about will effect you jetting.

[Eviltanker]

^^^^ Agree'd ^^^^^
I would rejet. A 152 and a 40 sound lean to me with what you have for mods. Also have you recently cleaned the airfilter? If it was dirty before when you did the original jetting and you recently cleaned it your jetting will be off due to the "clean filter" pulling more air now.

[Honda6sv]

I just did all that...everything is as if it were new...except the cough...I think ill try bumping the pilot jet up. See how that works. I guess I always thought it had enough fuel at idle...i dont have any major mods so i thought a 40 would be good enough. But ill try the 42...ill keep this thing posted. Thanks for all your help!

[Honda6sv]

PS...I really doubt there are any air leaks on this thing...all the boots are in great shape.