Pictures wanted: Air Box Mod

Most people here do NOT recommend the K&N filter. It lets in too much junk.


BigDR, you need to post what bike you got.

Add it to your signiture in your profile.

If you got the 400E its a different from S model :)

Congrats on the new scoot BTW

You mean a pic like this:


Hold on a second - now that my bike is in a million pieces, I can find out if the hole is really 3x3. I'll add a post in a few minutes.


The traced opening! Of course this size was custom determined for my setup from numerous dyno runs by Scott Beasley at International Power Sports in Baltimore. For those not familiar with the procedure, basically it goes like this:

You up the main jet, and cut some of the hole to get started. Then, run the bike on the dyno. Open the airbox cover (where you insert the filter) and tape the hole with duct tape mostly closed - down to just 1/2" or 1" square. Run the bike again. If the power came up, it was rich - it wanted more air. Go back and cut some plastic out of the hole in the top about the size of the opening in the taped over airbox hole. Tape the side hole over and get another baseline run. Then, open another 1/2" or 1" hole - run again.

You can see by this method that you are simply leaning the bike out with little cuts in the plastic to match the opening in the taped-airbox hole (that would normally have your sidepanel cover over it). Eventually, you get to a point where you have leaned the bike out to the mixture that provides the best power and an even dyno chart when the bike is shifted through the gears. You can also get to a point where the mechanic says, let's go up on the main jet - pull the carb and swap the jet - then its more dyno runs and air after that until tuned.

This is why people that take their bike to a technician and go through a day or two of dyno testing kind'a laugh at people that just change all the jetting and airflow characteristics (jets, pipe, airbox hole), go for a ride around the block, and suddenly exclaim that they have the "perfect" tune! What a joke!

Anyway, here is the airbox hole in actual size. Sorry, I don't have software to determine the actual hole area. Note that this setup is with a Dynojet kit and a Big Gun Racing system. Details of the setup and a dyno chart with the baseline is at:



[ December 07, 2001: Message edited by: Crazy Luke ]


all most people do is, yank out that rubber insert called a snorkel, opps i mean a "air silencer" then open up the hole to about 3inches by 3inches.

I also took the time to put a screen on, but I've yanked the screen off since. A 3"x3" hole is great.

click here on the link

oh and I moved the ignition module back behind it's posts with some zip ties. just ask crazyluke he will tell you to do the same for alittle more hp

[ December 07, 2001: Message edited by: Gyro ]

We did the job at Scott's house - he has a dyno at his house - pretty funny. He didn't have the analyzer there, so we had to do it the old fashioned way.

Would someone with a CADD package, or similar software, please check the image to get the area of the opening for me - I'm just curious.....

Crazy Luke,

you are cool, doesn't matter what the mixture is when you tune for POWER!

So how would you tune the bike if you don't have access to a dyno?

va3mod- The old tricks - Is there hesitation in the roll-on, pops/backfiring on roll-off, doing the old "kill the engine at speed + plug check," etc. I never had to mess with that stuff - Scott has tuned my last four bikes on the dyno. Before that, I ran stock with old - OLD bikes that I had like the GS750 and the KZ440.

quikrnu- Yeah - pretty simple really. The idle circuit is another story, but that's what the idle mixture screw is there to do. In cold weather, my DR-Z was getting a few pops on roll-off - turn the idle mixture screw to richen her up when she hits the idle circuit - no problem - pops are gone. On the power, I think most of the tune is the main jet and air - but I'll defer to those with greater knowledge (which is almost anybody). But even if, as BigDR noted, you are using a gas analyzer, you still make a change & retest, make a change & retest. In this way, you squeeze out a couple of "hidden" horses in there!

I told Scott about the numerous suggestions at the forum regarding the pilot jet changes - he said it could make a difference, that it was a bike-specific thing, that he would have to check it out with some tests before he would believe it. He suspected that if it made a difference with the Dynojet kit for the DR-Z that Dynojet would have included a new pilot jet in the kit. On the other hand, Baja Designs is including them in their jet kit, so perhaps they did some testing. He said for the vast majority of his tuning for Formula USA, they don't mess about much with the pilot jet(s).

The Dynojet kit setup that I have is different from what most are using at the forum, but not necessarily better. The kit comes with special jets and a new needle that are manufactured by Dynojet (or one of their contractors to their specifications). There is apparently some exhaustive research that goes into determining the flow characteristics of the jet and the taper of the needle for a specific application.

I think the difficulty is that the test bike used for Dynojet tuning is obviously not going to be identical to your setup. Dynojet didn't change the airbox or the pipe on their test bike, we did (Big Gun Racing, airbox mod, Twin Air filter). We had to go up on the main jet to one beyond what they include in their kit (supplied by Scott - I think it was made by Dynojet, but not sure). If you copy the Dynojet test bike, you would leave the airbox and pipe alone and use one of the supplied jets in their kit.

On something like the pilot jet, you can bet that if it made a difference for their kit, you know they would include it. After all, its racers that are buying their kits to hop-up their rides.

[ December 08, 2001: Message edited by: Crazy Luke ]

Here is a link to a considerable amount of DR/DRZ info (including airbox modifications):

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