Idle speed is adjusted by adjusting the timing. With the engine off, move the throttle from idle up to mid range or something of the sort while watching the arm "with the adjustment knurled SS screw" that goes up under the flywheel, no connection to the carbs.....this is your idle (via timing change) control. Now that you know what to tweak, here's how to tweak it:
Loosen the keeper nut and back it out to 650 +- 50 RPMs with a warmed up engine In the water, pushing the boat in F gear, and the throttle all the way down at idle.....from the Service Manual! Tighten the lock nut back down.
