If anyone really wants to know how far the KLX can be pushed, he needs to go back to the mid-1990's. That's when the KLX300R was being tweaked by a number of tuners from a soft trail bike into a hard edged race bike. Back then, tuners like Stroker did push the limits of this engine platform - bore, stroke, porting, valves, cams, clutch, carb, exhaust...anything that could be modified was. And the resulting machines were very fast, and very expensive. When the YZ400F came onto the scene, it was cheaper, faster, and more reliable, and came right from the factory that way; it spelled the beginning of the end for the KLX300 (and it's descendents) as a sensible platform for outright performance builds.

 

Until my theory on the quality flow to the air box is tested one way or the other, speculation on this or that mod effectiveness would be premature?

The small gaps that remain once the seat and side cover are in place are 'dirty' aerodynamically - narrow and high drag, with wiring, sharp bends etc that produce turbulence and more than likely inhibit quick mass flow to the air filter and probably total less in total area than the air box opening without the lid.

So, it wouldn't be a surprise if venting the air box produces noticeable change.

When someone gets the chance disconnect your air box boot or take off the seat and go for a test drive. A revelation may be waiting

 

The KLX's with CV carbs might not like running without the airbox. Many of them can be very sensitive when not having a decent dead air space to draw from...or at least some way to limit turbulence at the intake mouth of the carb. You saw it on some road bikes back in the day when the individual K&N clamp-on filters were popular. Some did OK with them, and some didn't. The slide on a CV carb generally likes dead air to draw from. Even some successful ram air setups with CV carbs usually achieved it by pressuring the airbox with ram air but by limiting direct turbulence right at the mouth of the intake of the carb.

 

Well, now that everyone knows about roller rockers and roller lifters along with some stuff about tappets, did anyone read about air flow in those articles?

Side note: if you want to know about the seat to air box stick a few ***** of Play-doh or clay in a few strategic spots where you might believe there may be minimal clearance to see just how much is there. Then figure the perimeter and multiply it by the height average you found to find how large the actual area there is to draw from.

In addition, some bikes react well to the added holes, others may get totally loopy. The DRz400 has something about a 3" hole that I've heard/read of, not owning one I never bothered checking it out. My Zephyr will react really badly to the removal of the air box. It is a pain to jet in for individual filters and really doesn't gain much if any. This was learned from one of the most knowledgeable 550 guys in the country. He tried it all. To run and gain takes 29mm smooth bores over the stock 32mm CVs. The CVs according to him are too large for the 100cc cylinders (ever hear anything like that before, around here), the air box actually limits flow to a manageable extent. They actually went smaller when going to flat slides.

 

Speaking of airbox related stuff, my bike never came with a lid. Good lord it is load puttering at 60mph. Has anyone bothered fiddling with the lid to increase air potential while still keeping the noise down a bit?

 

I don't think there is a way to increase air flow by putting the lid back on.

 

didn't figure it would increase, but what if you cut out a bigger opening? should be a happy medium hopefully keeping noise down just a bit.

 

I think you can get a kdx 220 snorkel to fit and it has a larger opening and eliminates the grumble (i like the grumble) or you can just drill and put those plugs in.

 

Yeah, this is the direction I went. When compared to fully open and the lid still on but with a bigger hole, the lid-on scenario did take the edge off that really loud drone. It's louder than one with a snorkel, but this was as small as I was willing to go for air volume. It also acts less like an open bucket when mud and water try to splash up in this area.

 

That's even bigger than I had figured. Just need to find a lid now...