There is a reason we cruise with Yamaha 2-stroke outboards. I can’t remember a single dinghy outboard that some time in its life it didn’t go upside down for a variety of reasons. It just happens. I know it won’t happen to you but it did to us. Two strokes are simple to fix with no permanent damage if they go under water.
Here’s the fix. Remove the spark plug(s) and pull the starter rope until spray stops pumping out the spark plug holes. Remove the carburetor, it's just two or four 10mm nuts or bolts, plus linkage and the fuel hose, depending on the engine. Remove the screws holding the float bowl and pour out the mixed gas and water. Remove the jets and use brake clean or CRC Cleaner Degreaser to blow the jets and passages clear. Reassemble the carb and set it aside.
Take a fresh water hose and flush the engine through the opening the carb was covering as well as the spark plug holes. Let the hose run for at least a full minute down the throat, and for a bit in the spark plug holes as you slowly pull the starter rope to get the salt water out from behind the rings. Replace the carb.
Clean and replace the spark plugs once there isn’t any more water coming from the spark plug holes. Remove and empty the under-cowl fuel filter and blow out the lines. Start the engine on fresh gas. The engine starts nearly every time on the second pull. It will sputter and smoke but let it run for at least a minute on a pair of hose muffs or in a five-gallon pail of fresh water. Shut down the engine, replace the plugs with a new set and start it once again. It will run smooth.
You aren’t done yet. It is very important to let the engine run for five minutes or more, in gear at high idle. Running in gear heats the engine which opens the thermostat to the top cylinder to flush that as well. Before we begin this five minutes of high idle under load, we launch the dinghy and tie it on the hip to let it run and generate some heat. Other times we have run the dinghy back and forth close to the boat, upwind and up current, of course, so if it quits you can row back easily. We’ve never had one quit, once the plugs were changed, but still…
Bottom line: If a four-stroke engine goes upside down it is bad. And it's unlikely you will be able to get it running, so it becomes a spare anchor and you'll have the financial thrill of buying a replacement outboard IF you are somewhere where they are available. Otherwise you be rowing.
With a 2-stroke you can fix it yourself. Small 2-stroke Yamahas are still available in the Bahamas. We’ve bought a number of them in Nassau over the years. Larger dinghy engines from Evinrude are still 2-stroke and available everywhere.
Have a great week, everyone, and enjoy your Christmas Holiday! See you next week!!!