Trim issue

[Hookmaster]

Occasionally my F100 slowly lowers when it is trimmed up. Is there a valve that needs replacing?

[ricqik]

You need to bleed it. There should be a screw on the side(left on mine) that you can loosen. When you loosen this screw, the motor will drop, so be careful and stay clear out of the way of the direction the motor will drop. Once it has dropped, press thr trim up for 15 sec and then down for 15sec. Do this for 2-3 cycles. Then tighten the screw back up and trim mtor up and wait to see if it still lowers over time. Before you start anything, fill the resevoir full first. If this doesn't work, you got a leak somewhere or a worn part within the trim system.

[boatfixer]

The screw ric qik is talking about is the manual release valve. Back it off and re-seat it. DO NOT OVER TIGHTEN! cycle it up and down a few times, check fluid level. If this doesn't take care of it, then you may have to take it in for repair.

[tlbigstump]

Most likely you have a leaky main valve,that's what causes most Yamaha's to leak down,there's a service bulletin out for this engine for this reason back from 02 I believe.