here's a strange one... 50 hp 4 stroke

engine is 1998, 4 cylinder, 4 carbs
good compression, new plugs, new fuel filter.
First off, the engine chuffs (sneezes) at idle. Then, when idling fine (or as good as it gets), it runs for a few minutes then all of a sudden out of the blue it picks up hundreds of rpm and stays there. There is no movement on the carb linkage.
Why would it (and how could it) pick up rpm like that? My first thought was that it was leaning out on the fuel or a vacuum leak. Can't find either one. Maybe not looking in all the right places.
HELP PLEASE! it's driving me nucking futs!

What have you done so far and did it run just fine before the latest maintenance was carried out ? Do you have a service manual available?

Sounds like a spark issue.----Use a timing light and see if you can find the cylinder that is kicking in.