is it bad to run my 400ex with out an air lid

 

Well if you run w/out the lid you are basically giving the bike more air to pull in. This is not a bad thing as long as it is jetted correctly and other mods that would benefit from having more air. i'm assuming by your sig that you have rejetted due to a K&N and slip on exhaust

2 other things to think about.

what do you mostly ride...(trails or muddin' )
and are you at a stock bore and a stock carb.


basically if you open the bike up to allow tons more air you will have to equal that w/ more fuel...
if not properly protected you engine will suck tons of dirt in and trash the head

its not bad if it is "necessary"

 

I agree with Duster.

 

No, but you will need a rejet. Not the hot setup if you run in mud and the wet.

 

Its already jetted with a K&N and FMF Powercore 4 and im onoly riding it right now when its cold out and the bround is frozen and keepen it out of the mud. I put back on when its realy wet and if is snows

 

You will still need a rejet! The limiting factor in your air intake system, is the size of that little snorkle that lets the air in. With the lid off, you are increasing the size of that opening something like 20X, and you will be getting tons more air.

Give it a try. Go out and pull the lid off, and see of it doesn't start harder and run bad, especially on the top end. Don't ride it for long however, because you will be running lean and that means hot, and that can damage your engine.

 

I been riding it without the lid, it starts as soon as you push the button even if its cold and it runs better

 

<div class="FTQUOTE"><begin quote>Originally posted by: steffen400ex
I been riding it without the lid, it starts as soon as you push the button even if its cold and it runs better</end quote></div>

.....then why are you asking.....
cold air is denser and will help an engine compared to 80 or 90 degree weather.
sure it will seem fine until you start toasting the rings and lighting up the exhaust valves....

how long have you been running the bike like this?
did you buy it like that?
what does the plug look like?

 

think about re jetting just for the colder weather as well. check the plug if its like a coffee brown the a pretty good mixture, black is not good the the plug and white is bad for everything. All the gas now contains ethanol so it might have a slight white tint to it but not chalky.