wont start and backfires

[SLSD400exGUY]

my bran new 05 400ex wont start anymore and it backfires. all i added was a k&n air filter with outerwear.


does anyone know????????????????????????

[cals400ex]

if the air box lid is modified, you need to rejet. i ran a 40 or 42 pilot jet when i was bone stock. you need to get a new plug probably too. when starting the bike, turn the choke on and pump the throttle a few times. then hit the start button WITHOUT hitting the gas any more. otherwise you will flood it and it will not start.

[SLSD400exGUY]

ok ill try that tomorrow

thanks

[yamablaster24]

like he said your jetting is way too lean. First try pulling off air filter and with choke on plug up the intake with your hand. If that dont work get a new plug and then try it. If it only starts like that and still back fires you need to jet for the air filter. AS it gets warmer it will be ok but when its cold its gonna be running to lean. Lean bikes are hard to start

[400exc]

well, i have only an air filter, why dont mine need rejeted? it starts easy in the winter, and easy in the summer.

But SLSD400exGUY, do you have your spark arrestor off when u try to start it? because mine does that sometimes when i try to get the carbon out of it. But yea, the plug is probably fouled, because when i fouled my plug once, it made one big "POW" when i tried to start it. I bet that is why you cant start it, just go buy a new plug, and see what happens.

[SLSD400exGUY]

well i found out that it was the sprak plug and i bought a new one today and it works lol ill wait to add the airfilter until i get a new slip on that way i can re jet it one time.