I bought my 2003 400EX last summer. This is my 1st bike so I'm new to everything about it.
Started my mods with a K&N Filter & then a WB Series E slip-on.
After installing the slip-on I noticed a HUGE difference in power! Very pleased!
However, when cold starting it now (after installing slip-on), it seems to run very rough, cutting out almost dying. Have to feather the throttle to keep it running for a few minutes before it can be left alone. Now, once it is warm it runs like a champ and like I said before the power is outstanding!!
Did nothing to the jetting, left it stock.
Do I have a problem with the cold start or is this typical?