If you are wanting to clean the combustion chambers, then there are some very good products just for that purpose. And they work much better than water or ATF or Diesel.

It's called something like combustion chamber cleaner or upper cylinder cleaner and is available at a lot of places. Boat shops use it all the time. I keep some of GMs upper cylinder cleaner to clean carbs with. Works better than carb cleaner and is water soluable.

This is the same stuff that JC WHitney used to call Tune-Up-In-A-Can. But it works very well. In fact, the outboard service schools recommend these products as the preferred choice to clean their carbs. So I have used this stuff instead of carb cleaner for 20 years. Seems kind of funny that a product that is designed for and does a good job of de-carbonizing combustion chambers is not very well known.

As to the question of whether that is the root of the OPs problem, well, maybe, maybe not. But it doesn't take much time or money to clean the combustion chambers and at least rule it out.