As some of you may know I bought a Honda 440ex a few weeks ago. This one is for anybody with any experience with a bored out atv, it doesn't have to be a 400ex I think...

When I bought it, it had the air box lid off of it. The previous owner said it was necessary for the quad to get enough air because of the big bore kit, but I thought he was a little nutty so I didn't take him seriously. Well I bought an airbox lid for it, and then did a high speed pass. The atv choked at about 3rd gear under hard throttle. When I took the lid off it worked fine.

So do I need to run this thing with the lid off? Or does it just need to be rejetted?

Thanks for the help.

 

Big bore need to be rejetted,thats how the fuel /air is adjusted not by air box mods.

 

I think its jetted fine, I just had heard that you need to rejet when you add/remove the airbox lid. I guess that's not accurate?

 

Is you air box intake restricted? When I jetted my street bike after just a pipe change it took 3 tries to get the jetting right.

 

Well it has a snorkel that makes it draw air from under the gas tank to keep mud and stuff out. I guess it could be a little bit restrictive. Would it make that big of a difference?

 

There is an ideal air/fuel ratio, and that is what jetting is intended to achieve. One does air intake and exhaust mods first, then adjusts the amount of fuel to match that amount of air, by changing the size of the jets in the carb. By putting the lid back on, you mess up that ratio and it doesn't run right anymore.

More air is usually better for performance!!! Sounds like you are properly jetted for the lid off. Unless you are running in the mud and wet all the time, it will be best to just leave the lid off like the previous owner had it. If you need to have a lid back on, then you will also need to rejet for the new reduced amount of air coming in....but your performance will suffer.

 

Any breather mod can make a difference. Alot of 440 kits have been installed,do a "search" on this site,never heard of air box mod needed but I never heard of a snorkeled 400ex either. Maybe your snorkel tube need a slightly larger Dia. 2" at least,what size tube is it now?

 

I have searched quite a bit on here... I haven't seen anything either. I'm all for more performance, and I don't run in mud much, but if I do leave the lid off I will probably get one of those K&N lids or something, just to help filter things.

The snorkel is equipped stock... the other 400ex I used to have, had the same part also. I'll do a quick search and see if I can't find the part I'm talking about...

 

Here is the 'Snorkel'
It is OEM, but I guess it really does work like the name suggests... So it probably would restrict airflow, wouldn't it?

 

If you want to use your lid you'll have to re-jet accordingly... probably about two sizes down on the main jet. You may have to make a small adjustment to the fuel screw, as well(1/2 turn in, or so).

If you want to leave the lid off, I'd suggest getting an Outerwears, EHS or K&N lid. I'd also ditch the snorkel and plug the hole with a lid from a spray paint can with this arrangement... they fit perfectly.