Sticking with the factory recommended 16:1 will help you sleep easy tonight. The reason the 5.5 and 7.5 OMC motors of this era need the rich mix is because they don’t have any needle, ball, or roller bearings in them, only sleeve type friction bearings which need the extra lube. Running them at high speed with a leaner gas/oil mix runs the risk of starving the bearings for lube and that in turn makes the crankcase too small for the connecting rods as they can seize on the crank and then break through the side of the block leaving you stranded without a paddle.
As stated, this topic can go on forever but when you think about it, these motors have probably lasted this long because of the amount of oil they drink. If the motor is well tuned and has decent compression, they will hardly smoke at all using modern TCW III oil. Smoke from any two stroke motor is usually more noticeable on startup, when the motor is cold, but goes away as it warms up.
