Check idle speed (see Idle Speed Inspection).
Remove the fuel tank and air cleaner housing (see Fuel Tank Removal and Air Cleaner Housing Removal).
Supply fuel to the carburetors with an auxiliary fuel tank.
For the models other than the California model, remove the #1, 4 carburetor vacuum hose plugs and #2, 3 carburetor vacuum hose fitting.
Connect the suitable pipe joints [A] to the carburetor vacuum hoses [B] and vacuum gauge hoses [C].
Install the air cleaner housing.
Connect the vacuum gauge hoses to a vacuum gauge [A].
Start the engine and let it idle to measure the carburetor intake vacuum.
If the vacuum is incorrect, adjust the synchronization.
Carburetor synchronization vacuum:
Standard: Less than 2.7 kPa (2 cmHg) difference between any two carburetors.