400ex Surging at high speeds

[Pennyyz]

I just got a 2000 400ex from a buddy and about half throttle its starts to surge real bad. When you shift it goes away till about the same rpms. Its kinda like its hitting the rev limiter but I know I am not even close to that rpm. Another friend told me that maybe its my timing chain streaching at high Rpm. could mu cdi box be messed up. The quad is all stock except the stock pipe has been messed with and its loud and sounds like Sh*t.Please Help.

what do u mean by surging? maybe its sumtin to do with your carb try cleaning it.

[Pennyyz]

By surging I mean it looses power for an instant then gets it back for an instant then looses it and so on

[turnandburn]

maybe the valvas floating.

[Martin Blair]

are you sure its not missing?

Mine used to miss about 3000rpms its the stock carb get a fcr or edelbrock with mine it went away runs great.

[Toadz400]

throw it away and get a polaris:rolleyes: ...lol jk

check out your carb, make sure it's clean and also make sure the main jet isn't loose or something like that...maybe you should pick up a new pipe too:huh

[Aceman]

How is it running when it's surging. Does it cut out or bog? Does it smoke when it surges? How is the power? Or does it still run alright except for the surging?

[hondaracer31]

Sounds like the baffles were removed from the stock pipe. They probly didn't change any jetting when they did that. It's probly a little lean. 400ex's are lean to start with, so if they messed with the pipe.............

[Bob-Hobo]

Check all the electricals, my 300 used to do that when the plugs to the coil came loose.

[660r2a400ex]

before you take anything apart, spray starting fluid on your boot that connects to ur carb while ur bike is running, if it starts to rev quicker their is a leak in ur rubber boots, replace them, if not take ur carb off and clean them.