I find the noise without the lid totally unacceptable. Without the snorkel, it's just unpleasant.
I suppose this is because i have the standard exhaust system and because I'm a sensitive soul

On my 250 EFI, removing the snorkel seems to make the midrange power feel a bit flat. I was very surprised how much resonance there is in the airflow when the throttle is opened, I expected a continuous sucking of air, but it sucks and blows remarkably strongly.
I have to wonder if the Kawa engineers know a thing or two about induction tuning.

My bike has the clutch switch mod and 1/2 MCM (only the inlet cam advanced). The 1/2 MCM does reduce intake roar and seems to give a less strangled feel to the low and mid response.

 

Since the previous owner removed the airbox llid, I took a pc of 1/4" plywood and covered about 3/4 of the box. I can't see any performance drop but I no longer hear the loud sucking sound when the throttle is open.

 

Interesting read:
http://motorcycleinfo.calsci.com/Airboxes.html

 

That's an interesting article, but as always, one size doesn't fit all. There is a lot of good info there, regardless. A couple of his observations aren't as concrete as he suggests. He pretty much states that an airbox/engine combination will not receive a performance gain by opening up the airbox, and in fact will suffer a performance loss. Well, there's a lot of "depends" in that statement.

He uses a V-Strom as an example which apparently has a large volume of air in the box. Most 4-strokes do like a large amount of dead air space to draw from as a general rule...except in the cases of well designed ram air systems...but that's another can of worms. Even for a 250, the KLX has a relatively small air space in the box, but it's probably adequate. What you have to be careful of when opening up the inlet on an airbox is doing it in a manner that causes highly turbulent air at the inlet or obviously a water hazard. The under seat location on the KLX is plenty safe as far as air turbulence is concerned.

Dirt bikes don't usually have the luxury of big air boxes with interiors that are highly conducive to optimum airflow. Many road bike boxes even have room for little rubber velocity stacks and other designs and devices that take advantage of air flow up to the carb or throttle body throat. The KLX has the typical plastic box made to fit in a tight confine with an exhaust pipe, frame members, and a shock all jockeying for space. The snorkel with its small opening and location on this bike is not a performance enhancement. It's to kill noise and match the emission jetted carb. I'd agree that little to no benefit occurs on a stock KLX with all OEM parts in place when removing the lid to the airbox...but I won't even swear to that.

The site referred to has some good information, but it probably doesn't go far enough in describing all the variables involved in the intake system of an engine. With many, maybe most, modern street cars and pickups, if you just go *****-nilly hacking up a well designed and purpose built airbox and intake system, you can very well upset the apple cart. Our KLX is neither modern or well designed when it comes to the airbox and intake design.

Something else to consider is that engines are all still what you generally refer to as an air pump. More air in and more air out...in the most simplistic terms...is good. But like the statements made in the site referred to here, exceptions exist all over the board in design and execution.

 

Yeah, what he said

 

I agree (I did not claim the article was accurate/applicable). I also hate ported speakers for their very poor transient response - moderately stupid idea to use resonance to extend bass - but that's another story.

The other concern I have with most of these articles and the power curves is that they are generally talking about WOT. I am more interested in throttle response and mid range power. At least the Kwacker doesn't (yet) use the dirty trick some car manufacturers use of mapping 90% of the performance in the 1st 25% of the throttle travel.

 

FIRST I've heard of this..

Can you fill me in please? any pics? or thread links?

Thanks!

 

Search "T" mod.
The carb has vents that hang down through the swingarm, when you cross a long stretch of water those vents can't breathe under water, shuts the bike down mid-stream.
Put in a T and run the line up high somewhere above the "waterline" and no more stalling on long river crossings, well until it gets above the airbox for an extended period.