I had 2 outboards, both of which became gummed up. I removed the carbs and took them to a local garage where they had an ultrasound bath, and cleaned all the jets ( charging the princely sum of £20). Both outboards now running and idling perfectly.
I now run them as usual on ordinary petrol, but at the end of the day unplug the remote tank and run the engine to a stop, then run from the inbuilt tank which has Aspen petrol in it. So far so good, but only done this for the last year.
Incidentally, I run my 4-stroke lawn mower on ordinary petrol, leaving the carb full of it season after season, and it starts and runs perfectly all the time!