Drilled my air box today..
 

And I think it's a winner! :eek:

I'd been kind of wondering why our air box moans and groans with the lid off .. and I thought well maybe it's just not getting enough air .. and the air that is trying to get in when there's no lid is fighting a lack of access through whatever gaps are there between the seat etc.. and creating a moan somewhere underneath

So I could either ride around with the seat off test the theory-or just go ahead and add some holes since I don't ride off road much anyway

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I didn't do an extensive test ride, but the bike runs like a raped ape (TM36 carb) at WOT ..and though there's a heck of lot of exhaust noise..I can't say I'm hearing any moaning out of the air box

Faster with the modded air box? I have to say YES..and as I left the house I was not necessarily expecting to actually feel a difference, but things seem to be happening a lot quicker now. Each time I went through the gears I was on the rev limiter in first gear before I knew what happened. - And of course I was accustomed to how quickly it was reacting previously so for me anyway that's a big indication of a gain in power.


I'll have to try it some more under varying load conditions to see if there's still a moan and review the SOTP change



:D

But i like that ground shaking grumbly intake growl! Haha but more power is sure tempting for something to simple...

I run without a snorkel but kept the lid. Over the years I have done your mod to many bikes, street and dirt one easy way to check if you really made a positive affect is duct tape as any and all holes can be covered then removed piece at a time until you get it like you want it. Never really thought about it on this bike but I am still a tad rich so you got me thinking....

Actually - I drilled the holes, then cleaned up the mess and went inside for maybe two hours before the short test ride. It looked like rain when I was done and I wanted to eat lunch and what-not. I wasn't even going to ride it but later decided to go get some fresh gas a mile away.

So testing the mod wasn't exactly first in my mind, which makes my sotp impression fairly unbiased - I wasn't expecting to feel any difference

As soon as pulled onto highway and started going to thru the gears at an average pace I thought that something felt different

I remember one post here somewhere that mentioned how much faster his KLX was with the air box to carb rubber boot removed during a test ride...

Maybe the air box isn't getting enough air?

I also have an XR200 and sometimes switching back and forth even days apart, from one that's slower than the other might alter true impressions, but I think my mind was wide open.

What if every mod that's been done to these bikes so far has been held back by restriction of air going into to the air box? It's not like there's advanced design going into air box engineering - every single cylinder bike is almost the same. From 80cc maybe on up?

Why doesn't the cam mod work on bigger displacements? Why the noise without the lid?


Someone who is already not using the air box lid and is at a dyno or racing a buddy needs to try it with the seat off sometime

Are you going to have to rejet now, with all that extra air?

Now that you mention it I had my boot not on 100% (couldn't get it to fit, kept slipping off) and I did notice it was tamed down once I got the boot completely locked down..

You'd think so wouldn't you? Unless it was already rich. I'm going to wait until my a/f meter arrives and save some guess work.

Nothing apparently wrong with the jetting right now. It's hard to describe the difference, but it's almost like when you richen up a bike that seemed to pulling well before you did it, and then afterwards it's obviously making more power at WOT

Or so it seems..


I'll put the lightened flywheel on later this week



I just ordered some Uni pop-in foam units that use a 1" hole.

Was going to suggest those. I have used them on my old XT350.

Richard, you've really got me thinking. I've been running with out the lid for so long assuming that would allow unrestricted airflow - now I'm not so sure. So I'm gonna take another look at it. As it is with the stock carb, I'm having to run the largest jet in the kit to get the A/F below 13. I've followed your posts carefully and know that your running the TM36-68. Perhaps that means opening the airbox more than just pulling the lid gives extra HP only available if your running a 68. That thought is fascinating. It means that, with a standard bore, there's even more reason to swap to a TM36-68 than ever before!
Seem right to you?

Oh, BTW, Richard..
The intake growl is caused by the standard cam timing and is fixed with the MCM mod. That I can confirm.
The reason the MCM is not recommended for the 351(IMHO) is that it moves the torque curve lower in the RPM range - maximizing volumetric efficiency at a lower range of RPM- at the expense of upper RPM torque. This is apparently not the best complement to the 351 mod due to the restrictions of the intake tract. In a nutshell, the 351 needs help in the upper RPM range due to a restrictive intake tract and that's where the stock timing helps the most.