Mercury - Troll Control Kit RPM Adjustment Control 8M0083437. The Mercury Troll Control Kit is designed for boaters who want simple, fingertip control over engine speed during slow-speed operation. It is commonly used on mechanical Big Tiller setups where fine RPM adjustment is preferred over constant throttle movement. The control mounts within easy reach at the helm and helps maintain a clean, uncluttered control layout.. Maintaining steady RPM at low speeds supports smoother trolling, control