Easy way to tell. A spark arrestor is a netting that prvents any sparks or hot objects to come out of your pipe. A method used by the usfs out on the trail do to those that take them out of the built in stock pipe, get a small stick and put it down the pipe, if it does not stop you have no arrestor, it should stop within a few inches if you do. You can find arrestors on just about any ATV web site. They can range from $60-$150. Dont read into the hipe that by removing you arrestor you will gain more power, it is not worth the usfs fine and or inpound fee until you replace it. I had a buddy get his impounded last weekend for removing his, and you will not get a any more power.