I have a 75 HP Mercury Optimax on my Tracker PT 175 TXW.  I love that combo, by the way!  It's almost a year old.  Recently, I've begun to have a bit of a problem.  Usually the first "run" it's fine.  After or during a later run, the engine guardian will kick in, limiting the RPM's to 3000.  There are no warning beeps.  After idling/chugging along for a bit, it will allow normal operation, but may kick in again.  The tell-tale stream seems fine.  The last time it did it, I felt the stream, and it was cool.  I don't know if that means anything, though.  It's time for it's checkup anyway, but I was wondering if anyone had any diagnoses or ideas.  Thanks.

sorry i have no idea, i did want to comment though that i have the same exact set up, 75 opti on the 175txw and i also, love it!