After a couple of days commuting with Marcelino's full cam timing mod applied, I was satisfied and decided to try the next step of removing the airbox lid. Note that I already have a KDX snorkle with the bottom extension cut off of it. Not much noise at all from it, but much improved airflow over stock.

Even with the cams positioned exactly as shown in Marcelino's first post and the mod working fine performance-wise, the airbox noise was something else starting at around 1/8 throttle on up after the CV slide began to activate. Lid removal did seem to wake up the bike a little more, however.

Nonetheless, after about 5 miles of testing, I already was getting a case of monkey butt from the thing because of airbox buzz, plus it was painful to my ears.

Therefore, to try and pick up a bit more air flow without the extra noise, I dabbed some black RTV around where the bolts thread into the airbox and then placed a steel washer at each hole and bolted on the lid. The idea is to give a little bit of gap between the lid and the airbox for a touch more airflow than before. Kind of like a calibrated leak around the airbox lid.

It definitely kept the air box noise down on the 2nd test ride. Performance may have been better than direct bolt on of the lid but it could also have been psychological.

I think Marcelino originally started his mod to try and quiet down excessive noise from the airbox. I also think he is running the stock filter, which is definitely of thicker and denser foam than my Uni. Could that be helping dampen the noise a little for his situation?

Until tonight, I have never run the bike with the airbox removed so have no reference.

Your opinions and ideas count.

 

kansas, I think there is some merit in modding the lid in some fashion. I cut a bigger hole in mine after running with it completely off, and I think the roar is noticeably diminished. I think the more you can introduce something over the airbox top, you disrupt the sound waves. Here's a pic of my mod. I don't think it takes much disruption to help reduce the noise. I'm thinking the more of a maze you can make to disrupt the sound, noise is reduced. Air can flow around all manner of curves and corners, but sound is more strongly affected. You see this in lot of more modern automotive intake systems. There's not a lot of room to work with on the KLX to convolute the intake opening, but just about anything seems to help. My mod doesn't look like much, but anything to bounce around the sound waves seems to help.

It's interesting you didn't notice the strong noise reduction mentioned before. Is there any reason a carb would be different than FI like Marcelino's bike has?

 

I too briefly tried running with airbox lid removed, but the throbbing sound was too much for my eardrums. I ended up with a compromise as well. I removed the snorkle, and then drilled about couple rows of 1/2 holes (about twelve or so total) over the filter element to let in more air while still breaking up the sound waves. Seems to work well. The bike was just a touch more perky with the lid completely off, but I just couldn't hack it. I figure, the way I've got it, I can still run the snorkle for those really wet rides, and strip of duct tape is enough to seal up the holes if I think it'll help to keep the water out.

 

Kansas-KLX: thanks for sharing your washer idea. I am going to see if I can fine-tune my intake any further this way. I currently run a simple 'no-snorkel' set up. In my experience, totally removing the lid caused some stumbling and increased off-throttle popping. I also like the 'splash-guard' effect of the lid when doing river crossings. Intake noise is not a factor for me due to my Two Bros pipe which renders all other sound inaudible!

 

You guys should know that the EFI bikes do have quite a lot more intake noise . The reason is that the throtle body only has a butterfly in it , there is no slider that would gradually rise like in a CVK carb . With the cam mod the noise on MY bike is less than half of what it used to be , it transformed from unbearable to noticeable . Many of the newer bigger bikes are drive by wire : when you turn the accelerator you only turn a sensor , the control over the butterfly it´s done by the ECU . There are mixed versions of this , two throtles in series , one in your hand , one controlled by the ECU .
Anyways , if somebody does not want air vibrations to be transmited to the plastic part of the seat I think a better solution would be " soudproofing " the plastic of the seat : glue a piece ( a little bigger than the top of the air filter ) off that dense sponge that is used under the sleeping bags . It normally is about 1/2 " thick .

 

Holy cow! How many db must that intake put out in stock form? If mine last night was only "noticeable" then I shudder to think what "unbearable" must be like. You must have been bleeding from your ears.

 

A common mod for 4 wheelers is to cut a portion of the lid out and cover it with material that acts like a prefilter but allows air thur without restriction and still provides some splash guard properties. You might check it out.

 

linkin, I tried out that approach too. I obtained some Uni dense pre-filter material and made a cover to fit under my opened-up lid. I figured it would be a good pre-filter and maybe a noise depressor. I was a little surprised when it didn't do much of either. My air filter seemed to get just as dirty during the same time period and level of use and dust exposure as it did without the lid pre-filter. I noticed no sound deadening. I notice more when I remove the lid vs. using my modded lid. Perhaps the lack of noticeable pre-filtering benefit was the biggest surprise.

 

I've got a buddy who runs a pre filter over a k and n on his 4 wheeler and the filter itself always looks new pulled for maintance. I have no experience with the lid mod where you make a big window and cover it with fabric but I've seen others do it alot.

 

Yes, I agree that a prefilter system like the UNI setup for our bike is effective when it makes contact with the inner filter...K&N or foam setups. I think the physical contact between the two mediums is what contributes to the pre-filtering effectiveness. I can see why people would try the pre-filter material over the airbox opening like you mention. I thought it would be quite effective. I was somewhat surprised to see how ineffective it was. And I used actual UNI brand pre-filter material and not just some piece of foam from inside my barcalounger...LOL! It looks like the same density foam as the red outside pre-filter that comes on the 2-stage UNI filter for our KLX.