My new 400ex doesn't run right! After I get it started it continues to backfire and sputter. Sometimes it will run great for 5 minutes then will stall. Then it's back to sputtering and backfiring. This thing is new, should it be doing this? I Don't think so. Maybe any of you knowledged 400ex'ers can help. What could it be? What should I do?

 

I don't know if this still applies, but the 2000 400ex and maybe even the 99's throttle cable was way out of adjustment, there was too much play. Check this on yours. Also, check that your muffler is tight against your head pipe. This happened to me when I got my aftermarket pipe. There was room for air to get in and it caused it to backfire. This being a new machine, you shouldnt worry about that too much. Hope I helped.

 

I talked to a few people and they said it could be the carb, running to lean. Could this be.

 

I doubt it . There definitely is something wrong so take it back to your dealer right away. Mine is 2 years old and it has never backfired yet.

 

Does it backfire inthe exaust or the carb. If ti backfires in the exuast its to rich and if it back fires in the carb its to lean. I would check the air cleaner. If it looks alright I would take it back to the dealer and tell them what its doing. You should have at least a 6 month warranty from the factory. Good luck

 

I don't mean this to be smart. But make sure your choke isn't on.

 

Are you using the choke correctly? Your choke has three positions, do i need to go on?

 

I'll admit i left the choke halfway once and it did exactly what your talking about. Just check it out.

 

What kind of pipe do you have on your quad? Is it jetted properly? If its not jetted properly for the altitude your riding at or its not jetted at all it could backfire like that