How to rebuild the TRX Racing carburetor
Sometimes the carburetor can be damaged from abuse, can be gummed up from long term storage, or could simply develop wear from normal use and require rebuilding. This article describes step by step the process of carburetor disassembly and reassembly. The carburetor can be rebuilt by replacing the body and O-rings, or simply cleaned thoroughly to free it of debris and oil which can prevent it from flowing fuel or tuning properly.
Tools and materials required:
-1.5mm allen wrench
-2.5mm allen wrench
-8mm open end wrench
-Small slotted screwdriver
-Can of compressed air (shown) or Nitro Cleaner*
(*Available at local hobby shops- do not use automotive grade carburetor cleaner- it can damage the soft parts and composites.)
A replacement carburetor body with O-rings (Traxxas part # 5234) and a carburetor o-ring and seal set (Traxxas part #5247) can be purchased from a local dealer if the current body is damaged, stripped, or worn. Otherwise, the body may simply need to be cleaned to work properly again. Use the exploded view for obtaining part numbers for any other damaged parts you may find.
Remove the high speed needle assembly from the carburetor using the 8mm wrench and unscrewing the brass base. Inspect the parts for bends, wear, clogs, or debris and clean if necessary.
Unscrew the two aluminum plugs with a 2.5mm allen wrench. Inspect the red O-rings for nicks or creases which may hinder proper sealing.
Remove the throttle arm using the 1.5mm allen wrench, noting the arm's original position. Next, remove the blue dust boot. Inspect it for tears or cuts
Unhook the return spring from the carburetor body. Be careful not to damage it. Rotate the spring around the body until the spring is out of the retention groove.
Remove the idle stop screw by unscrewing it completely and pulling it out. Inspect the screw for bends or torn O-rings. Now you can pull out the carburetor slide.
Once the carburetor is completely disassembled, inspect the components once again for any damage. Inspect the carburetor body for stripped threads, inspect the idle setscrew bore threads, and check for cracks. The low speed mixture screw (still inside the slide) can also be inspected if you suspect it may be damaged.
If the carburetor body is in good condition and is just clogged or dirty, use canned air or Nitro Cleaner to thoroughly clean the body inside and out.
Reinstall the aluminum plugs with their O-rings, and install the high speed needle assembly. Be careful not to overtighten the brass needle base and strip the body! Before tightening the brass needle base, you can angle the fuel inlet to the desired angle to allow easy hookup of the fuel line.
Reinsert the throttle slide and spring assembly as shown, and carefully screw in the idle speed screw being careful not to overtighten it. Make sure the groove in the slide is present to allow the screw to be seated. NOTE: You must install the slide into the carburetor body before inserting the idle speed screw. Do not force the screw if you feel resistance! You can adjust the idle speed screw's final position later.
TIP: Put a light coating of after run oil on the O-rings to help ensure a good seal and prevent tearing of the O-ring during assembly.
Reinstall the return spring making sure the spring sits in the groove of the carburetor body as shown.
Reinstall the blue dust boot over the slide and body. Make sure it seats flush against the body. Reinstall the throttle arm, and install the carburetor base O-ring.
Check for smooth operation of the slide, and reset the carburetor mixture screws and idle screw. Using the small screwdriver, carefully screw the High and Low speed mixture needles in clockwise until you feel resistance (Do not overtighten). From there, the stock settings for the 2.5, 2.5R, and 3.3 engines are as follows:
High Speed Needle: 4 turns counterclockwise
Low Speed Needle: 1.5-1.75 turns counterclockwise
To set the idle speed screw, adjust the screw to where the opening in the carburetor is about 1mm wide as shown below:
Reinstall the carburetor in the engine with a new air filter. Start the engine, and retune the engine for peak performance after it has warmed up to operating temperature.