what is the point of the spark arrestor? Does it muffle the sound in any way or improve performance. Is there a stock one on the quad allready?

If you look at a stock setup the black oval piece attached to the end of the muffler is the silencer right, and is the stock spark arrestor built into that?

Does anyone use a heavier primary spring with there RCR or use a spark arrestor? Why?

 

Spark arresters are just that, they arrest the spark. Machines without spark arresters will shoot flames out of the pipe. This is not good, as it can easily start fires. The spark arrester stops the flame...or spark, from exiting the machine.
If you want to ride in any national forests, you must have a spark arrester. Actually, most public places require them now.
When I do order my RCR kit,(almost seems like I never will at the rate I am going) I will be adding the spark arrester to it.
Your stock muffler does have a spark arrester. All original stock mufflers have them.

 

My ATV has a stock spark arrestor pipe on it...most and I think all quads do, am I right?