i removed my box lid, do i need to jet it? its a 300ex by the way

 

Yes you will. You are taking in about 200% more air.

 

How can a motor take in more air than the displacement will allow? Won't it run the same no matter if the lid is removed or not? Isn't the hole in the carb the limiting factor?

 

When the air box lid is on, the hole that the air is allowed to go into the filter is only about 1 1/2" wide. You remove the lid, the whole is now about 4"x8". Go take your lid off and see how it will run. Why do you think people jet there quads?

 

<div class="FTQUOTE"><begin quote>Originally posted by: budedm

How can a motor take in more air than the displacement will allow? Won't it run the same no matter if the lid is removed or not? Isn't the hole in the carb the limiting factor?</end quote></div>

If that were true, it was sure a stupid move on your part to take it off....becasue all it will do is get your air filter dirty about 10X faster (not to mention all the water you are going to get in there)!!!

The hole in the airbox, is way more restrictive than the hole in the carb. So, yes you will need a rejet, if you didn't what you have done wouldn't make a bit of sense, would it!

If you have a stock muffler/header, that has now become your "limiting factor". The header on the 300 is pathetically small! Get an FMF PowerCore 4 or Q, and it will come with a high flow header.

Don't ride it until you get the rejet, because it will be running lean (hot) and can toast your engine!

 

I run an EHS Racing airbox lid with Outerwears. At least it keeps out the big stuff, and I ride desert so water isn't much of an issue.