FMF now has new "modular" end caps for the PowerCore IV. I like to clean my spark arrestor screen about every six months. With the old style cap, you have to drill out the rivets, clean the screen (which is part of the end cap), and rerivet the endcap back in place. With the new modular units the endcap bolts on, and you can remove/replace the screen or endcap just by undoing three screws. Also, the new modular system has the option of changing end cap sizes. 2" is standard, but there are 1 3/4 and 1 1/2" options, for different powerband characterisics. Larger end caps tend to give more high end power, and the smaller tend to give more low end throtle response. There is also a "quiet core" available, but with this installed you might just as well have kept your stock mufler.

You can replace your old style endcap by ordering a "bulkhead", new endcap(s), and screen. The bulkhead rivets into the end, and the endcap and screen are held to it by 3 screws. You will have to drill a couple of holes, and widen two of the old holes to make the bulkhead fit, but instalation isn't complicated, and you only have to do it once. I like lots of low end response, so I'm going to try the smaller endcaps (which are currently backordered). When I do, I will post my results.