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How to Balance Synchronize Motorcycle Carburetors

Many motorcycles have multiple carburetors providing power for the engine. In a multiple carburetor system, one or more carburetors may fall out of adjustment, or synchronization, with the others. This causes the cylinder to receive a different amount of air and fuel than the others and create an imbalance in the engine. Poor power, hesitation and bad fuel economy may result. You can make a mechanical adjustment to ensure all carburetors work at the same time and same rate.

Instructions

1

Place the motorcycle on the center stand. Start the engine and allow it to warm up until it idles reliably. Do not allow it to reach full operating temperature as this may lead to overheating.

2

Shut the engine off. Turn off the fuel supply petcock at the gas tank and remove the fuel line at the carburetors. Remove the hold-down bolt at the rear of the gas tank and lift the tank off the motorcycle. On some models, it may be necessary to remove the seat or side covers in order to remove the gas tank and access the carburetors.

3

Remove the vacuum plugs from the carburetor bodies. Some motorcycles have rubber caps press-fit into vacuum ports; others have screw-in plugs that require adapters that come with a multi-port manometer kit. Select the proper adapters and connect the vacuum lines from the synchronization tool to the ports on the carburetor bodies. On motorcycles with more than two carburetors, match the numbers on the manometer ports to those on the carburetor.

4

Hang the auxiliary gas tank from the handlebars and connect the hose to the carburetor gas line inlet. Place the portable fan in front of the engine and direct the air flow over the engine to keep it cool. Turn the auxiliary gas tank cut-off valve to the "On" position. Ensure the fuel hose is not touching against an exhaust pipe or the engine.

5

Start the motorcycle and observe the readings on the synchronization tool. The carburetors must be adjusted if the gauge reads more than 2.4 inches of mercury between any two or more units. Locate the adjusting screws for the carburetors. Some models have the screws located between the carburetor bodies; other models require the removal of a top cover to access the adjusters.

6

Identify the base carburetor. On any multi-carb system, one carburetor is considered the base piece and is not adjustable. All other carburetors can be adjusted to match the base piece. The base carburetor is normally identified by having the throttle cable and idle speed screw attached to it. Turn the adjusting screws on the other carburetors one at a time until the readings on the synchronizer are within 2.4 inches of each other. Tighten down any lock-nuts, making sure the adjustments do not change.

7

Repeat the previous step for every carburetor on the motorcycle. Open and close the throttle a few times and recheck the readings. When all readings on all carburetors are within 2.4 inches, tighten all lock-nuts and replace any covers or other devices that were removed to access the adjuster nuts. Set the final idle speed to the manufacturers specifications and shut down the engine.

8

Remove the auxiliary gas tank and synchronization tool . Remove any adapters and replace the vacuum port plugs or caps on the carburetors. Replace the gas tank, side covers or any other component that you removed.