I just bought a used 1985 Evinrude 15hp motor (E15RCOB) that had been sitting around for a long time. I've only run the motor for a little while, and as far as I can tell everything is going fine, but the throttle control is very stiff. I took the handle off thinking I would find something there, but it seemed like the handle just connected with a screw to a rod that adjusted the throttle. The rod was just as stiff without the handle on it as it was with the handle on. I found a couple of grease fittings around where the two gears connect (#65 and 66 in Leeroy's Ramblings Picture), but putting grease in there didn't help much. There aren't any broken teeth on the gears yet, but I have a feeling I might break some soon if I can't figure out how to free up the controls.
http://leeroysramblings.com/OB images/twist grip.jpg
http://leeroysramblings.com/OB images/twist grip.jpg