400ex wont start

[mitchamus]

04 400ex. stock engine. will not start just cranks. was just warming it up kept back firing when giving some gas, sometimes flames out of the exhaust. took it for a quick spin again not running right.
shut her down now cant get it started.
Spark plug???

[nickk]

That's what it sounds like to me. what's your jetting and the temperature outside?

[blasterandy]

Sounds like a really bad jetting problem. No, its not a sp prob. I would be willing to bet ur high on jetting. I would throw about a 15* in there and see if that works however. Some more detail on elevation, and temp would really help. also i would rep. the spark plug u prolly fouled it NGK=dpr9z(i prefer ngk) Autolite=4163(cheaper but $hit imo)

[kjbula]

Ok this just happened to me and I found the problem yesterday. Let's start with me putting on a HMF s/o 2 weeks ago, changed the jetting to 152 main 42 pilot needle in 4th position from top. Put it all back together and it was harder than normal to start and when it finally did start the motor was poppin' and crackling. It was late and I wasn't going riding for a while so I didn't mess with it any more till last Saturday. I removed the carb checked the jetting just to be sure, it was fine (no loose jets) needle is in good condition. I CHECKED THE CHOKE LEVER AND THIS IS WHERE I FOUND THE PROBLEM. The choke lever seemed to work fine but the butterfly was not moving in the carb so I removed the choke and noticed the sping was off keil. Put it back together without the choke (remember to plug the hole with something secure) and my 400ex runs better than she has ever run. So in short, take the carb off and see if the butterfly thingy moves when you move the choke lever. Sorry so long...hope this helps.

[mitchamus]

its an 04 original plug. HMF sport slip on. temp around 70 in cleveland, oh. JEtting was fine when all last year.
i was hoping just bad gas and a fouled plug. Ill pick up a plug 2morrow. also will look at the choke to make sur its working correctly