With the demise of the 2-stroke motor modern outboards have changed, mostly for the better, though I am still a great fan of the simple and sturdy 2-stroke. Putting aside the significant environmental advantages, 4-strokes provide two additional pluses: increased fuel economy and no need to mix oil with the gas. However, these two advantages bring with them a couple of possible pitfalls.
First, that tremendous fuel economy we love in a 4-stroke--often burning half as much as a comparable 2-stroke--means that very little gasoline is being burned at idle. Sounds great, right? The problem here is that to meter that tiny bit of gas the slow-speed jet inside the carburetor is really, really, teensy. The inside of this jet, critical for a proper fuel/air mixture, is very easily plugged or fouled by the weensiest bit of crud. And, the typical outboard on a dinghy does not have much of, if any, fuel filter between the tank and the motor.
Inevitably means that if you aren't meticulous in filtering the gas as it goes into your tank, and then meticulous in keeping any crud out of the tank, including water, eventually that low-speed jet will get plugged and/or some other critical passage in the carb. In my experience, this will happen--it is only a matter of how long before it happens. I can almost guarantee that if your newish 4-stroke outboard has become harder and harder to start, and maybe doesn't idle all too well either, it is time to take that carb off and clean it, and it is time to seriously think about putting in a quality inline or fixed mount filter. It is not a crazy idea to consider putting a large, spin-on type of engine filtration set up on your dinghy transom.
However, even with this level of care, we sometimes must leave the boat longer than we would like. Today's gasoline is often laced with 10% ethanol and this gasoline is just not very durable. In my experience you only have about 30 days before it starts to deteriorate. And that's where the second pitfall emerges. The addition of 2-stroke oil in the past actually provided some stabilization of the gasoline mix as well as providing needed lubrication. The way around this is to add some fuel stabilizer to every tank of gas, whether 2- or 4-stroke. I have been using red StaBil for years with good success, but I now use the blue marine-grade StaBil that also claims to be better with ethanol gas. Adding this to your outboard tank will also help prevent phase separation--a condition where you get a layer of ethanol/water mixture with a layer of gasoline over. Once this happens you have to get rid of the whole mess and start over with fresh fuel. It goes without saying that you should be extra careful to keep water and moisture out of your gas, especially when it contains ethanol.
Do these two things and you will find your new 4-stroke outboard will keep running better and longer, but you still must be prepared for the inevitable carburetor cleaning periodically. This should become a routine maintenance item if you have a 4-stroke, and I highly recommend you learn how to do it yourself and that you keep the needed tools and parts onboard.