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View Full Version : idle problems when cold and its coughing



bmf400ex
10-07-2003, 10:56 AM
got a stock 400 cept for a T-4 slip on and a k&n air filter with outerwear.
when i got this last year in maybe july i think, it pretty much ran like ****. so i took the carn off and the guy had all kinds of ****ed up jetting.
anyway onto what i have done. I put in a 42 pilot, kehin 158 main and clip on 3rd groove. air/fuel screw at 2.5 out.
question i have is how can u tell the difference between a dynojet needle and a Kehin needle without having the two side by side? and does the stocker use a plasic washer underneath the top hat?

now onto my problem. it flat out won't start for ****, but if you pump the gas 3 times then hit the button its fires instantaneously, then immediately dies. I can do this all day long until finally some small heat has been generated and i hold the throttle with just the slightest amount of pull(it has a 1/4 turn throttle). once i finally get it started, the carburetor coughs and jumps like its lean as hell. its almost an artform to start this SOB, but i have come acustom to doing it. once i do this meathod about 5 times she is getting warm enough to run for a couple minutes all while the carb coughs and sputters. keep in mind i am holding the throttle just with the slightest touch of my hand. If i let off it will die instantly. obviously one would assume its lean issue, but once its warm it run almost perfect. and i might add when the engine has been warm, as soon and i touch the starter button it will fire up and idle beautifully. while riding it seems to be very strong from bottom to top, with a small hesitation in the low to low-mid section.
like i said once warm i don't have any complaints.

my concern is the carb sputtering and coughing and the hard starting, could a hairline crack in the boot cause this? if so one would feel that while on the gas hard. though ever once in a while i get ther occasional cough or sputter from the carb after its warm

sorry for the winded post but i try to put out all the info up front.

bmf400ex
10-09-2003, 09:03 AM
bump

cals400ex
10-11-2003, 01:05 AM
it sounds like your having some problems. a dynojet needle will probally have 6 adjustments ( i think) on the needle where the stock needle only has 5. also, the stock needle will say B44A on it. i would also check the mainjet. the keihin mainjets will have a K on them. this K almost looks like a star. this will determine if your running a keihin main or a dynojet main. a 42 pilot jet is fine. turn the fuel skrew out 3 turns or so. i would just go and get a new spark plug. that could be your starting problem. the stock needles dont have a washer underneath them. a 158 main is too big with just a slip on and filter. i would use a 152 in the summer months and a 155 in the winter months. good luck

10-11-2003, 07:09 AM
Take the bottom off clean everything and make sure the white plastic washer is not outa whack. Your jetting sounds OK. I know when it's cold here, i have to crank it a time or 2, and once it does fire,,i'll lightly hold the thottle down for about 30 seconds or so,,let off and it runs fine.