I just bought a 2002 honda 400ex the guy said it ran awesome and then he took it up to around 5000 feet and it was running rough so he adjusted the carb and it ran great
but then he brought it back down to sea level and it is hard to start and when it does start it idles spractically and when you give it gas it wants to die. I think it is getting to much air but how do I cut down the air that it is getting. I can't find the screw on the carb.

 

Maybe your anti-freeze is getting into your cylinder!!LOL j/k
When he adjusted for higher elevation he made it richer. If he did this by changing jets then you'll have to change them back. If he just tweaked the carb, then re-adjust it LEANER. The air is thinner at higher elevation, so it doesn't suck the fuel in as well. To compansate for this you richen up the fuel mixture. I heard that the dial-a-jet is pretty good if you change riding elevations frequently.
Check out October Dirt Wheels. Third question in dialed in section.

 

He did not rejet it because he told me that he did it on the trail. Do you know where the screw it to adjust it back done.
Also when I finally get it to run it runs good except for when you try to get in the throttle to go it starts choking out until you
let off on the throttle.

 

lol dirtwheels for the win [img]i/expressions/face-icon-small-smile.gif[/img]

 

Well speaking of choking out make sure that ain't on or stuck then find out how many turns out it should be. Turn it all the way in, then count those turns out. You may want to look up info on your carb, you may be able to find a pictur pointing that screw. Should be a brass screw on side of your carb.