How to Ensure A Dirt Bike's
Air Box to Intake Boot Seal is Not Leaking

On ANY dirt bike, it's of utmost importance that the air box to intake tract is sealed, otherwise, you'd might as well not run an air filter as the engine will be drawing in dirt and other abrasive particles through this opening, so this page has been created so you can be sure your intake tract isn't drawing in unfiltered air.

If you were cleaning the air filter and looked into the intake tract as suggested in the article on servicing an air filter and you DID see dirt, water or foreign particles in your intake tract, that's not good but hopefully you found this page in time to save your motor.

If you've seen dirt, water or foreign particles in the intake tract and you're pretty certain that it is coming from the air box to intake boot junction, this article will show you how to do something about this.

Who Needs to Know This?

This article is primarily directed towards those whom have seen water or dirt in the intake tract but these tips can also be applied during replacement of the intake boot and it's advised to follow the steps outlined here whether you're upgrading to a Tassinari Tunable Intake or you're replacing the boot because of a puncture, crack or tear in the boot allowing unfiltered air to be drawn in to the intake tract.

Additionally, these steps are good to perform as a preventative maintenance technique for someone who hasn't yet seen dirt in their intake tract.

Note: Some dirt bikes do not need this procedure to be performed due to the advanced designs of the intake boots and air box construction making it practically impossible for unfiltered air to be drawn in at this area with the exception of a clamp being loose or the intake boot not being properly installed.

The best way to determine if an intake needs sealed is upon disassembly; If the intake boot has a lip that extends inside the air box as well as outside, or if there is only a flange extending from the air box where the intake boot attaches and it's secured with a large diameter clamp, then sealing the air box is not usually necessary although doing this can't hurt and doing so will give you peace of mind that no unfiltered air carrying dirt, sand or other fine particles will ever enter the intake tract here, as well as you'll be certain that water will not be able to enter the intake from this area while washing the dirt bike, or if you encounter a wet track or trail.

How To Disassemble the Air Box And Prepare the Parts for Reassembly

With the exception of the Yamaha YZ450F and YZ250F, backward engine design, to do this properly you're likely going to need to remove the subframe and air box as an assembly but before getting started, you should ensure that the area around the carburetor or fuel injection throttle body is clean before beginning disassembly and this is best done by washing the motorcycle before continuing, otherwise during disassembly, dirt or other particles could find their way into places you don't want them which includes the path towards the motor.

  • With a clean motorcycle, begin by removing the seat and subframe from the motorcycle with the air box attached.
  • Once the subframe / air box assembly has been removed from the dirt bike, remove the air box from the subframe for easier and better servicing abilities.
  • Once you have just the box with the intake boot attached separated from the subframe, disassemble everything removing the fasteners and clamping pieces to enable removal of the intake boot from the air box.
  • Once the air box is fully disassembled, clean any remaining sealant or other stuck on adhesives from the pieces, then clean all the parts using a cleaner such as simple green which is available at most auto parts or home improvement stores along with a stiff brush followed by rinsing well with clean water.

How To Inspect the Parts and Properly Reassemble the Air Box

  • Begin the reassembly by using compressed air to dry all the parts you just cleaned, then lay everything out in a clean area so they're ready for reassembly.
  • Now with everything clean & dry, be sure to closely inspect the intake boot and all the associated parts while looking for any cracking, holes or tears in the areas that are critical which would include anything from the air filter to the motor.
Should anything appear damaged, Never try to repair it no matter how small or insignificant the damage appears.

A damaged intake boot cannot be repaired and should only be replaced. This means whatever kind of JB Marine Tex Epoxy you had in mind is not going to hold, and if you do try it's going to look ghetto. Your just going to have to order a new or used part to replace it with.

Anything you try to do to repair a damaged intake boot will never last due to the intense vibration that a dirt bike generates and mixed with the presence of fuel, this will cause any sealant to work itself loose in short order with the sealant you applied likely being drawn into the intake airflow, possibly resulting in fuel induction or motor problems along with another air leak which will allow unfiltered air along with all the other things you don't want going into your motor to be drawn in which is what you are working to prevent.

Once You Have A Clean and Inspected (or Replacement) Intake Boot

There are gasket kits available designed to seal the area you are working on, but 3M Weatherstrip adhesive that is available at most any auto parts store is what we use, and it works great for the following steps.

No other type of silicone or sealant is recommended for this other than 3M Weatherstrip Adhesive, as the presence of fuel will likely dissolve any other sealant causing it to be drawn into the air stream which will then create an air leak and again, potentially lead to fuel induction or engine problems.
  • Begin by reassembling the pieces while applying a generous amount of 3M Weatherstrip adhesive to the areas where the intake boot contacts the air box.
  • Next install the clamping pieces on either side and tighten the fasteners evenly in a criss-cross manner while the sealant is still wet.

Don't worry about it if sealant gets on the threads of the clamping apparatus (which is also the air filter sealing flange) as this will help lock the threads while preventing loosening of these fasteners in the future due to vibration.

You want to see the sealant being forced out of the areas where it is applied when everything is tightened together as this will let you know that enough of the weatherstrip adhesive has been applied to create an effective seal.

  • Now allow the weatherstrip adhesive to fully dry, then carefully use a razor knife to trim away any excess sealant that has been forced out and is exposed to create a clean look, then reassemble the motorcycle.
Finally, ensure that the air filter is clean and properly oiled, then re-assemble everything and consider this thing worthy of the worst.

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