Dead 400

I have a stock 2002, 400 EX And it won't start. Everytime I call the dealer were i bought it they tell me change the plug. When i do it will start right up. it runs fine all day long, but after it sits a few days it won't start. change the plug and it fires. this changing the plug everytime I want to ride is gettin old. Someone please help.

turn the gas off after riding.

i turn the gas off whenever i'm not riding. I got into the habbit of doing so after ownin a yz 125 you could never leave the gas on unless it was running

[MIKE400EX]

Sounds like a weak spark. Check coil, spark plug wire, voltage to coil, coil ground, spark plug boot (corrosion?) etc.. What does the plug look like after the ike sits for a couple days? Maybe the fuel shut-off is not really doing it's job?

The plug is really black and wet.
but it still sparks

[MIKE400EX]

But it may not spark under the extra load from the compression stroke. Put a new plug in, ride around for a while and pull the plug. If it's black and wet you've got a carb problem. If the plug looks good and is not wet, put it back in and let the bike sit for a couple of days (w/the fuel shut off). Take the plug out before even trying to start it and see if it's wet. If it is then fix the shut-off valve. Or you could shut off the fuel, disconnect the fuel line to the carb and see if it continues to drip. Also make sure the vent on the gas tank is not plugged, if it is it will build up pressure and may leak past the shut-off valve. You probably need to change your oil by now too. Just some rambling ideas!

[4punksdad]

full choke until it fires up...........then half choke until it is warm........sounds like the jetting might be a little too rich. Open up the airbox lid & let it breath.

[400exRacerX]

If the plug is black and wet your way too rich. If the bike is stock you either are riding it with the choke on or your air filter is over oiled.