Honda Outboards BF40A/BF50A Service Manual, Page 427Get this manual
BF40A-BF50A 9) Hold the power trimtilt assembly upright and bring the oil level to the lower edge of the oil filler portLoosely tighten the oil hole cap10) Move the piston rod from the fully compressed position to the fully extended position two or three times by operating the power trimtilt switch11) Push the "UP" side of the power trimtilt switch again to extend the piston rod fully12) Remove the oil cap bolt and check the oil levelIf the level is low, add ATF with syringe or equivalent tool until ATF flows out of the oil filler port13) Install the new a-ring on the oil cap and tighten the oil cap to the specified torque[2]