no need to touch the muffler! It's designed to run its best just the way it is. YS motors have alot of torque and will eat plastic spinners. I think we all have learned this the hard way. I have a 14x8 apc with the plastic backplate fused to the prop(and the hole is now about halfway between the center and the edge!) still sitting on my bench from a few years ago as a reminder. The new Great Planes spinners with aluminum backplate works great!.
After the first tank you can go almost to the optimum settings on your needles(just a hair rich!). Otherwise you are doing nothing for the motor. Also after the last run of the day and you empty the tank, put the glow back on and run the motor dry! No need for afterun oil. Good luck!