Honda CB360 / CL360 / CJ360 Carburetor Synchronization Tool Kit
Everything you need to synchronize the twin Keihin CV carburetors on your Honda CB360, CL360, or CJ360 in one kit. Carburetor synchronization balances vacuum between both cylinders so the engine idles smoothly, accelerates cleanly, and delivers full power. This kit uses a single-gauge method with a gang valve to read one cylinder at a time, giving you a more accurate comparison than a dual-gauge setup where the gauges may not read identically.
Why You Need This
If your CB360 / CL360 / CJ360 has any of these symptoms, the carburetors likely need synchronization:
- High or erratic idle speed
- Inconsistent idle that won't settle
- Shaking or vibration while accelerating
- Mediocre throttle response or lack of top-end power
Most Honda 360s have not had their carburetors synchronized since they left the factory in the 1970s. A proper vacuum sync is one of the most effective tune-up steps you can perform on these bikes.
Specifications
| Wrench Type | 8mm socket with internal flat head driver |
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| Fuel Line | 3 feet of 5.5mm line (Honda spec size) |
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| Vacuum Line | 5 feet |
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| Vacuum Port Nipples | Brass, made specifically for the 360 carburetors |
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| Target Idle Speed | 1,200 RPM (Honda factory specification) |
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| Gauge Scale | Centimeters of mercury (cmHg) |
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Important Notes
- Prerequisites: Synchronization should only be performed after the cam chain and valves have been adjusted, ignition timing is set, and carburetors are clean with air filters in place.
- No air leaks: The carbs must have no air leaks from the diaphragms, intake manifolds, or throttle shaft ends. Air leaks cause false vacuum readings and make an accurate sync impossible.
- Engine temperature: The bike must be warmed up to operating temperature (about 10 minutes of riding) before synchronizing. Carburetor adjustment should only be made when the engine is at operating temperature.
- Keep it cool: Use a box fan pointed at the engine during the process to prevent overheating while the bike is stationary.
Kit Contents
- Sync Wrench (8mm socket with flat head driver)
- Vacuum Gauge
- Gang Valve (2-way, for switching between cylinders)
- Dampening Inline Valve (steadies the gauge needle)
- Carburetor Vacuum Port Nipples × 2 (brass, 360-specific)
- 5.5mm Fuel Line — 3 feet, with splice adapters × 2
- Vacuum Line — 5 feet
- Zip-ties × 8
How to Synchronize Your CB360 / CL360 / CJ360 Carburetors
- Remove the brass screws from the synchronization ports on the front/bottom of each carburetor, near the intake manifold. Thread in the brass vacuum port nipples from the kit.
- Run vacuum line from each nipple up to the gang valve. Connect the dampening inline valve between the gang valve output and the vacuum gauge.
- Move the fuel tank back slightly — extend the fuel lines using the splice adapters and 5.5mm fuel line provided in the kit.
- Start the engine and warm it to operating temperature. Set idle to approximately 1,200 RPM with the throttle stop screw.
- Open one side of the gang valve and read the vacuum on that cylinder. Close it, open the other side, and read the second cylinder.
- If the readings differ, insert the sync wrench into the synchronization screw hole between the carburetors. Use the 8mm socket end to loosen the lock nut, then turn the flat head driver to adjust the screw until both cylinders read the same vacuum.
- Go back and forth between cylinders, adjusting until the readings match. Tighten the lock nut when finished.
For detailed setup instructions, read our Knowledge Base articles: CB360 / CL360 Carb Sync Setup Instructions and How Do I Synchronize the Carburetors on My Honda CB360 / CL360 / CJ360?
Frequently Asked Questions
Why does the kit use a single gauge instead of two?
A single vacuum gauge with a gang valve gives you a more accurate comparison between cylinders. When using two separate gauges, the gauges themselves may not read identically, making it difficult to tell if your cylinders are truly balanced. The single-gauge method eliminates that variable — you read one cylinder, switch the gang valve, and read the other on the exact same gauge.
What does the dampening valve do?
The dampening inline valve restricts airflow slightly to steady the gauge needle. Without it, the needle bounces around with each intake pulse and is difficult to read accurately. Closing the valve partway smooths out the reading so you can see the actual average vacuum.
Can I use this kit on a CB350 or CB450?
The sync wrench, vacuum gauge, gang valve, dampening valve, and hoses work on the CB350 and CB450. However, the brass vacuum port nipples in this kit are made specifically for the 360 carburetors and may not thread into other models. The CB350 and CB450 use different vacuum port fittings.
How often should I sync the carbs?
Synchronize the carburetors any time you adjust the valves, replace the cam chain, clean the carburetors, or replace the intake manifolds or carb diaphragms. If the bike develops a rough idle or poor throttle response after running fine, a sync check is a good first step.
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Last updated: March 2026
