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Airbox Mod


Original writeup by JoeV

Edited By Chuck Sirois


Suzuki tried to make these l000cc twins easy to ride for all types of riders and placed some restrictions on the ignition and the air intake system. On this page we tackle the de-restriction of the air intake system.

The mod comes in two phases (coming from my project management days), "Phase One" being the flapper removal. This phase is imperative to peak performance. In my eyes this is a must! The second phase, "Phase Two" being the base plate cutting is less important and not necessary.

Phase One


First take off your drivers seat and then remove the steering damper. Then prop up your tank to expose the top of the airbox lid.

The flappers close off the air intake at low RPMs in 1st and 2nd so that the bike is not so jumpy. Really this robs performance. Remove the flaps and the actuators and adhere a metal or plastic disc to cover and seal  the left over hole as shown below.


Once this is done you should remove all the supporting vacuum lines. If you are uncomfortable with this step you can go ahead and securely plug the flapper (actuator) vacuum lines.

In the above diagram of the vacuum system the lines in red and the components with a red dot on them are now useless and can be removed. You will want to plug the line off the throttle body as denoted by the black dot on the red line. Also tape the VCSV electrical connection. Yes it is OK to remove the VCSV, VD and, VTV can all be removed.

Phase Two

BEFORE YOU CUT: This mod is kind of controversial. There are a lot of factors when it comes to aerodynamics of the inside of the airbox. Cutting the base plate does open up a bigger airway but may create more turbulence inside the airbox that can actually RESTRICT air flow.

From here, with the airbox lid removed and modded you should be looking at the air filter:

Remove the screws that are circled in the pic above and set the filter aside. CAUTION: BY REMOVING THIS FILTER YOU ARE OPENING THE ENGINE. ANY OBJECT DROPPED INTO THE OPENING CAN SEVERELY SHORTEN THE LIFESPAN OF YOUR ENGINE! Once removed you should see:

Remove the screws circled in the pic above. CAUTION: UNDER THE THROTTLE BODY FLUTES (the metal holes in the pic) ARE "O" RINGS. CAREFUL NOT TO DAMAGE OR LOSE THEM! In this step you are removing the base plate that we are going to modify as roughly shown in red below:

Your base plate should look like this when you are done modding it:

Put everything back and you are done!


Below are the original JoeV instructions -THANKS JOEV!!


 Joe V's Airbox and Base Plate Modifications
Information originally posted at
  Hi guys. As you know, you have requested information on the modification that I have performed on a number of TLR's. Due to the number of requests I have chosen to do it via e-mail so that I don't put up an extremely large post. I would like to first tell you about these changes. I have tried several ideas posted by people on the net, I first removed the flappers, and then I ran with the lib off the air box. What I found was that when I used either of these ideas, my bike would not make red line in 6th gear. I was given and idea by Hermit The Dragon about removing material from the air box. I studied this idea and thought that it could be improved upon. I know I have been given credit for this idea by a number of guys who I have performed this mod for but again, I cannot take the credit. I only modified an existing idea. I have spoken to a number of very knowledgeable persons on this subject and can only tell you what I have been told. I have no dyno available to me so I cannot support any claims with dyno sheets. The first issue is ram air. Many will tell you that ram air will only provide about 2 or 3 hp. I have been told by a friend who is employed by Yosh that ram air can provide as much a 10%. I also asked a fellow that was running a dyno at the Canadian Sportbike Rally last summer, he too stated that ram air can provide as much as 8 to 10% hp. With this in mind, I decided to try and maintain ram air well allowing the bike to breathe better. By modifying the air box and maintaining the lid I am easily able to pull to red line in 6th gear. If this is a result of a 2 or 3 hp gain I would be amazed. On all of the bikes that I have done to date, all had the TPS set incorrectly, and all were re-mapped to +5 +10 +5 with the mixture at 11 o'clock. It is my personal belief that it is the combination of all of these factors that has led to the dramatic results. My bike will power wheelie in 3rd gear and will pull strong to red line in 6th. I am glad that I have read similar result from the people that I have helped out. This modification does require the cutting of the base plate inside the air box and is therefore irreversible without purchasing a new base plate. I will draw up a set of instruction today and send them out to all that inquired. I think you will find similar results. A good number of us have.
  I have broken down the air box modification into 2 sections, the lid, and the base plate. Below are listed the steps to modify the lid:
  • 1.) Remove the air box lid
  • 2.) Turn the lid upside down
  • 3.) You will see the 2 air intake valves. These will be removed.
  • 4.) Slide the actuator rods out of the flappers (indicated in lid-1 jpeg)
  • 5.) Turn the lid over and locate the intake air control valve actuators (indicated in lid-2 jpeg)
  • 6.) Turn the actuators and remove from the air box lid.
  • 7.) Take one of the vacuum lines that run to the actuators and form a loop to the "t" fitting in the vacuum line.
  • 8.) Now all that is left to do to the lid is to seal the holes left by the vacuum actuators. On the bike that I have done, I use fiberglass disks, washers really, with gasket maker, and place one disk on the inside of the opening and one disk on the outside of the opening and secure with a 1/4" bolt and self-locking nut. It is important to seal these openings.


  Ok guys here are the directions for the modification of the base plate. It is very simple to do. You will require a rotary tool with a cutting bit.
  • 1.) Remove the air filter (illustrated in figure 1)
  • 2.) Remove the base plate by removing the screws (indicated in figure-2)
  • 3.) Cut away the material outlines in yellow in figures 3 and 4. Be careful not to cut the towers that the filter bolts to. Also if you turn the base plate up side down you will see that there is a lip that seals to the bottom of the base plate, be careful not to cut this.
  • 4.) Reinstall the base plate and filter. Reinstall the air box lid. Check the TPS adjustment. Re-map to +5 +10 +5 and you are done. You should now be able to reach red line in 6th gear.

As I indicated in my first letter, this modification has been done by others, it is nothing new or exciting. It does however work! It is my belief that most people underestimate the effect that ram air has on a bike. Once again, a fellow I know who is employed by Yosh and the fellow running the dyno at the sportbike rally, both indicated that ram air can increase hp by 10%. I tend to believe this as the end result has to be greater than the 2 or 3 hp claimed by some. Running with the air box lid off only produces hp in the mid range and detracts from the top end. This modification along with the re-map produces healthy increases in the mid range as well as on the top end. Good luck.

Okay, I went through Joe's procedure and took some pictures along the way. Hope this helps you all understand it even better. I haven't remapped my bike yet, but plan too. It seems to be running great without it for now, but I'm sure I could see an improvement in HP when I do. 


The first step is to remove the airbox lid and take off the flappers and valve actuators.

The next phase is to plug the actuator holes. I sandwiched the hole in the lid with two washers, a bolt and locking nut. Also, using some sealant to ensure it's airtight.

The pictures below show the airbox without the baseplate. As you can see the holes where the ram air enters are evident. I modified the baseplate to open these holes up. Joe's instructions are modifying the baseplate even more and removing the "wings" remaining on the plate, with the exception of the screw holes. I don't know there is an obvious benefit to doing this as the ram air will not enter through there anyway. If you study the picture, you'll see what I mean.

The next set of pictures show the airbox with the modified baseplate and filter installed. It also shows you the lid installed again. Of course the remaining step was to loop the hose at the T piece.

All information and images were taken from had no participation in the creation or write-up of this modification.