Engine trim tab setting and trim problem

[MLerner]

Cruising in my 1993 18 OMC 351 this weekend, noticed that during high speed runs engine ever so slightly trimmed down on it's own (that is, toward "bow down" on the guage). What could cause this?

Also, I noticed that the trim tab on the outdrive was set at No. 5. The operation manual says No. 3 is the optimum. What do you experts think? Thanks.

[Formula Jr]

Check your fluid level at full trailer up then, run thru complete extention and retraction on the drive about nine times in a row.
Then see if it does this again.

Alot of things effect where your torque tab should be set. Different props, level of corrosion etc. Does the steering wheel pull to one side or the other at WOT?

[MLerner]

Thanks for the advice on the drive. As to the steering, she seems pretty even. I guess I'll leave it as it.