Stock 400 EX with no airbox lid?

[timewass]

Will running my stock 400 EX without the airbox lid make it run lean enough to do engine damage? It has stock exhaust and jets. I noticed a slight power increase, but I've also noticed that sometimes it will backfire just a bit then shut off. It fires right back up, but it concerns me. I also have a new plug to put in, but can't seem to find a socket that will fit..... What's the trick to changing the EX's plug?

[Razorback]

it does sound like you are running a little lean. if you do it long enough, you'll eventually cause damage.

the best way to change the plug is to use the socket that comes with the toolkit attached to your quad. i've heard of a few other sockets working, but not many. you might do a search on this site for 'spark plug socket' and see what you find.

[knighttime]

400ex's come lean from the factory according to the service manual. You are making it run even leaner with the lid off the airbox. Some bigger jets will help ya out.

[timewass]

Thanks for the info... the person I bought it from was running it with a large (2.5"x 2.5") hole int he top. I didn't like the sound it made so I removed the lid completely. Should I just get a new lid and not cut it all up?

I'll search on 'spark plug socket' to see what I find. Cause I know none of the sockets I have will fit.

Thanks

[timewass]

I suspect it's running lean because the engine is very warm. Ok... i know an engine gets hot, but it seems too hot to me. If I leave the air box lid off would it help for me to lower the clip on the needle one notch to richen things up a bit?

[Wheelie]

Lowering the clip would be a good idea, also increase the main jet size to a #150 (stock is #148).

get a new lid and buy those air vents with the sponges in them. They let in more air but keep out water and debris.

[timewass]

I failed to mention something.... my elevation. I live in western, PA and the elevation where I ride varies between 1800 and 2100 feet above sea level. I put my airbox lid back on and bumped my main up to a 150 from the store 148. I did not notice any difference at all. Any suggestions? Is it pussible to get more power by jetting my machine?

[Wheelie]

The only ways you're going to notice a power increase from jetting is if the quad is jetted improperly, or mods are done that require a jetting change to keep things running smoothly.

If the airbox lid is left inplace/unmoddified, stick with the stock jetting. If there are concerns about running lean, turn the mixture screw out 1/4 to 1/2 turn.