please help

[TRX45OR]

my little brothers 400 ex is cutting out it seems like its only when he mashes the gas, it has a yosh/jetkit/k&n we took off the air box lid stoped cutting out but started to back-fire whats next.thanks

[cals400ex]

i need to get some more info from you:

whats the elevation you ride in?
what the temperature you ride in?
what are all of the mods to the bike including air box lid on or off?
i assume your running dynojets, not keihin jets?


my hypothesis is that it is a tad bit rich for the conditions either on the needle and/or mainjet. what happened when you removed the lid is leaned everything out but not the pilotjet/fuel screw is too lean so now it backfires on deceleration. answer these questions and we will try to help.

[TRX45OR]

dinojet yoshi pipe # k&n im not sure about elevation but right now is 89 degrees and humid now the quad has had these mods for a wile now and this just started happening. oh ya rev limiter checked that too put the stock one on and same thing:confused: :confused: :confused:

[400ex28]

:bandit: :confused:

[cals400ex]

i would try around a 155 dynojet. i hear alot of people running the needle in the 3rd clip position but i have never tried these jets before. i would pm ewalker on this site. he uses dynojets, along with others here, and has good success. my guess is that he will even tell you to run a smaller mainjet than this.

i would try to clean the carb out and even change the plug.

[TRX45OR]

thanks dude