Honda Outboards BF40A/BF50A Service Manual, Page 54Get this manual
HONDA BF3!5A45A
CARBURETOR SYNCHRONIZATION
Start the engine and allow it to warm up to normal operating temperature1) PIece the outboerd motor on level surface end move the shift lever to "N" position2) Remove the three 10 mm plugs from the intake port of each cylinder
31 Attach the vacuum gauge adapters to each plug holeConnect the vacuum gauge tubes to the adaptersNOTE
Connect the vacuum gauge No1 tube to the No1 carburetor adaptor, vacuum gauge No.2 tube to the No carburetor adaptor and the No.3 tube to the No.3 carburetor adaptor properly