Make sure the release valve is snugged up.
Motor will not stay trimed up.slowly falls after raising it up. Checked fluid it is full. Motor is still under warranty but hoping it was something I can do my self
What year is it? Is it one of the 2.1 liter 4stroke engines? Some of the earlier 2.1 liter Mercury 4strokes had defective trim units that would leak down. There was also a problem with some of the failing to trim down when under load. I had to have the unit on my 2015 model replaced due to not trimming down under load. When it stuck I'd have to come of plane to get it to trim down. I haven't heard of many problems with them lately.