Note that Avgas is LL meaning low lead. The spark plug will need cleaning every 10-15 gallons or so. You may also want to open the engine up at that time and check for cleanliness/build up. With good carb settings it should be clean inside.

To be sure of no build up with any gas engine, Every 10 gallons or so, you may want to run a gallon spiked with injector cleaner 2 ozs per gallon. Really keeps the heads and pistons clean.