Honda 350 Carburetor Tuning

Introduction

This tutorial will guide you through the process of tuning the carburetor on Honda 350 and 450 twins. Proper carburetor tuning can resolve issues like hesitation, popping, backfiring, and overall poor performance. By following these step-by-step instructions, you can adjust the throttle cables, synchronize the carburetors, and fine-tune the idle mixture and speed to ensure your motorcycle runs smoothly.

Step 1: Adjust Throttle Cables

1. Locate the throttle cables: Find where the throttle cables connect to the carburetor and the throttle grip.
2. Check for slack:
   • Twist the throttle grip and observe the cables.
   • There should be minimal slack in the throttle cables.
3. Adjust the cable tension:
   • Use a 10mm wrench to loosen the lock nut on the cable adjuster.
   • Turn the adjuster clockwise to tighten or counterclockwise to loosen the cable tension.
   • Aim for about 1-2mm of free play at the grip.
4. Re-tighten the lock nut to secure the adjuster in place.

Step 2: Synchronize Carburetors

1. Prepare the bike: Ensure that the motorcycle is on a level surface and warmed up to operating temperature.
2. Connect a sync gauge:
   • Attach a synchronization gauge to the vacuum ports on each carburetor.
   • Make sure the gauge is calibrated and functioning properly.
3. Adjust the synchronization:
   • Start the engine and allow it to idle.
   • Observe the readings on the sync gauge.
   • If they are not equal, adjust the throttle stop screws on each carburetor until the gauges show matching readings.
4. Recheck after adjustments: Turn off the engine and disconnect the sync gauge.

Step 3: Set Idle Mixture

1. Locate the mixture screws: These are usually found on the side of each carburetor.
2. Turn the screws:
   • Start with the screws set at 1.5 turns out from fully seated.
   • Start the engine and let it warm up.
3. Adjust for best idle:
   • Slowly turn the mixture screw in (clockwise) until the engine begins to stumble.
   • Then, turn it back out (counterclockwise) until you find the smoothest idle.
4. Repeat for each carburetor to ensure both are evenly adjusted.

Step 4: Set Idle Speed

1. Locate the idle speed screw: This is typically found on the throttle linkage.
2. Adjust the idle speed:
   • Start the engine and let it warm up.
   • Turn the idle speed screw clockwise to increase the idle speed or counterclockwise to decrease it.
   • Adjust until the engine idles smoothly, ideally around 1,000 RPM.
3. Confirm stability: Make sure the idle is stable and does not fluctuate.

Conclusion

By following these steps, you can effectively tune the carburetor on your Honda 350 or 450 twin, addressing common performance issues. Regular maintenance and tuning can enhance your motorcycle's performance and longevity. For further assistance or to gather tools and parts, consider checking out resources like Amazon. Happy riding!