The throttle on my 2001 225hp Optimax has a very hard to operate spot just as the plastic/nylon roller on the throttle body lever starts to move away from the closed position on the cam (even with cables disconnected). The roller appears only slightly worn and I can't really tell if the cam is worn. I plan to replace the cam and roller in hopes this solves the problem. anyone have similar experience or able to sujjest alternative cause?

Is it hard with the throttle cable from the boat disconnected?
If not look at your shift and throttle cables.

Throttle is hard even with cables disconnected from motor.

Something is out of whack for sure, the whole setup moves very freely when it is right.
Fortunately you can disconnect the 2 linkage rods to isolate what is stiff.
The throttle butterfly will move freely just by moving the roller by hand.
Process of elimination is the only way.

Got my son to operate the throttle while I observed the throttle linkage more closely and found the problem. The throttle position sensor and it's linkage were binding. Disassembled the linkage and shifter and cleaned some very minor salt build-up and all works fine now.

Good boating.