400ex engine problem?

[DominicD400ex]

2004 400ex.

ENGINE = STOCK and never opened up.

Haven't done any fuel/intake/engine mods for at least the past ten hours of riding.

Today i'm out putting around just in the yard since i have no skidplate and it's running just fine. Put it away, and then get it back out an hour later, and it won't rev past 1/3 of the way and it won't take any more than 1/3 gas or it just dies. There's no oil leaking out of the top end, and it runs okay as long as i'm super soft on the throttle and in the low rpm's.

It doesn't LOOK like i blew a head gasket.

Any input guys? I know my way around an atv, but inside the engine is something i'm new to.

[dariusld]

Choke on?

[RIDEREDson]

its choked or low on gas

[DominicD400ex]

Neither. Those were my first two thoughts.

It acts that way with the choke all the way off, and it had a half tank of fresh gas.

Tomorrow I'm gonna yank the airbox off, maybe something's going on in there, i'll clean the carb too.

I just don't understand why it would happen all of a sudden when it was running fine before.

[RIDEREDson]

Next check out the carb. Sounds like jets are clogged or dirty.

[<DRS>GPF]

Originally posted by RIDEREDson
Next check out the carb. Sounds like jets are clogged or dirty.

X2

[bigd's ex]

I agree with the jetting issue. I had the exact same problem, but mine ended up being the 2 screws on the bracket that connects to the slide came loose & 1 fell out, keeping the slide from opening up all the way, creating the problem your having. Might want to check that out when you have the carb off.

[DominicD400ex]

I haven't had time to get it apart yet, but i've been thinking the plug may be fouled. If the gap's a little too big, it could run fine in the low rpm's but not keep a spark once it got up there.