Honda BF20A-BF25A, BF25D-BF30D Outboard Motors Shop Manual., Page 244Get this manual
Engine speed does not decrease- Throttle cable sticky
or inter-
Check the throttle cable for restriction or interferenceReplace: (P13-21)
Throttle arm or rod not move smoothly
Engine speed increased excessively and it fluctuates
Boat and propeller mismatched causing overrev of the engine
I Propeller bushing rubber slip-
Replace with the correct propellerReplace the propellerReplace the propeller
Setting of outboard motor incorrect (Transom height, tilt angle, etcincorrect)