I've had many ABC/N engines and broke-in many, too. I've seen new out of the box ABC/N 'fits' vary somewhat...even in the same size/brand. Some new ABC/N engines are fairly loose when new...I've seen others that are tight as #ell. I'm thinking the way the late George Aldrich taught me...an ABC/N engine needs to be ran just richer than full lean for the first two minutes. I'm thinking he knew what he was talking about since he was one of few people to re-chrome cylinders and re-fit pistons to them. EVERY ABC/N engine I have ever ran that way from new has lasted a LONG time. I never have second-guessed his opinion by doing otherwise...I guess 'downunder' is going to see what could, or will, happen by running this type of engine as it is 'not supposed to be ran'. The results should prove interesting.