Plugin,
Here's something important that needs to be said. If you run your engine a click or two rich it will last a lifetime. But it only takes one lean run to ruin an engine completely. Tune the engine for the best running and then richen it up a click or two. You should see a small trail of smoke when flying. I always run my engines just a bit rich and I have engines with 500+ flights on them. But one flight with the engine running lean and it can be ruined forever.

Ken