Honda BF20A-BF25A, BF25D-BF30D Outboard Motors Shop Manual., Page 269Get this manual
3) Attach the vacuum gauge adapters to each intake manifold plug hole and connect the vacuum gauge hoses to the adapters Connect: The No.1 vacuum gauge hose to the No.1 vacuum gauge adapterThe No.2 vacuum gauge hose to the No.2 vacuum gauge adapterThe No.3 vacuum gauge hose to the No.3 vacuum gauge adapter
t11 VACUUM GAUGE ADAPTER, 0.8 1201- (3) 07510-3000100 or 0.8 50L (3)
VACUUM GAUGE (Commercially available)
4) Start the engine and adjust the idle speed (P3-2)5) Clamp the two SE joint tube using the commercially available tube clips keeping away from the tube protectors as shown[2] SE JOINT TUBE B
[I] TUBE PROTECTOR
Avoid clamping on the tube protectorsWarm up the engine sufficiently before clamping the SE joint tubesDo not clamp the SE joint tubes with the engine cold, or it will cause poor start of the engine6) Check the intake manifold vacuum difference between the cylindersTake the maximum reading