My dad went fishing the other day and everything was all good until he went to change locations. He said his motor wouldn't run above 2000 rpms, had to idle back to ramp. Any ideas as to what the problem might be?

Guardian mode, somethings wrong and the computer is trying to prevent further damage, need to get it checked out.

two common problems with optimax

oil tank float bad --replace engine oil tank

overheat at high idle ---place restriction in cooling return line

both problems will put into guardian mode

Random but any chance you've got too small of a cranking battery? That threw my opti into a tailspin this spring.

This may not be related to his problem but two things that can cause problems and both are inexpensive to fix are : change the fuel filter and make sure your fuel hose and bulb are working properly, holding pressure and not collapsing, thus starving the motor for fuel.
Also make sure the line isn't kinked and free of all obstructions.

Similar thing happened to my 2014.....it was a bad coil.

As stated above guardian mode it could be a lot of things my has went into it a couple of times once when I shifted into gear theres a button(lack of what to call it) that tells the computer or brain what ever you call it its out of idle mine would stick and it thought it was still in idle,and once I hit the rev limiter trying a new prop a couple of time and it went in guardian mode, they can be tricky to find but a dealer can by hooking it up to a fault code machine.

Yep. My guess too

On my last boat (2005 Cougar w/225 Pro XS) it went into guardian mode when I sucked some sand or gravel up and it stuck one of my thermostats open. One side would reach normal operating temp and the other would stay cold. Triggered the guardian mode. Replaced thermostats and was good to go. Cleaning them probably would have fixed the problem but decided to replace then. Good to go on the next trip!

Thanks for the input, the motor is out of warranty but only has 110 hours, hopefully it's an easy fix and not a blown power head.

UPDATE!! Dad took his boat in and they ran diagnostic test and it ended up being a bad coil. Thankfully nothing major, he's had a tough go on boats the past few years so this was a big plus. Thanks for the help.

Outstanding

Coil is easy to diagnose and change. Anybody with any mechanical ability can do it. Go to auto parts store and get an in line spark tester and test each coil. You can YouTube it.