ORIGINAL: Gene Chernosky
Since this engine came with an OS 'F' plug when new it would be a good idea to stick with it.
I disagree. When I got my first OS 120 Surpass, it wouldn't idle below 3500RPM. All the "experts" at the filed told me to stick with the F plug--no mater what.
I ended up using an OS #8 plug in my Surpass--but only after wasting boatloads of money on several F plugs.
Every engine is unique. They all get broken in differently, and at different temps and rates of expansion. Just because it's an OS 4-stroke engine doesn't necessarily mean that it needs an F plug.