Traxxas TRX 2.5, 2.5R, and 3.3 engines can be equipped with one of two different HSN Housings. When purchasing
it is very important to choose the correct tuning dial for the correct HSN Housing.

Generally the older engines have the 6mm nut and the newer engines have the 8mm nut. The HSN assemblies are
interchangeable from engine to engine and cannot be determined simply buy the engine size.
Revo 3.3 and other Traxxas models may require a small adjustment to the carburetor orientation to complete the
installation. Unscrew and remove the HSN from the housing. Place the dial over the housing tube. If the head interferes,
loosen the carburetor pinch bolt and rotate the carb until the dial will slip past the cooling fins. Rotate just enough to
clear the dial and re-tighten the pinch bolt. Reinstall the HSN and adjust it until the top is just above the dial face. This
should place the needle approximately 3 to 4 rounds from the seated (closed) position.  Actuating arms and throttle
linkages may require minor adjustments to compensate for the new carburetor position.
    The different HSN Housings can be easily determined by looking at or measuring the hex nut with the appropriate
wrench used for loosening and tightening.
6mm hex nut
8mm hex nut
Use tuning dial part# NT102
Use tuning dial part# NT103
On some models loosening the HSN Housing a small amount (about a round or less) will allow enough tilt for the dial to
slip down past the cooling fins without any prior modification or carburetor repositioning. After the dial is in place the
housing is re-tightened.
Will need to rotate the carburetor a small amount.
Carburetor rotated to clear the cooling fins.
Installation Note: