We got our hands on a FMF stainless steel Factory 4.1 RCT full system and bolted it up in less than fifteen minutes. Installation is very simple, but you will have to use your existing stock heat shields (FMF does offer carbon fiber heat shields for $99.99) and use some hardware that FMF provides to bolt on the rear can. The FMF system provided slightly less exciting throttle response, but gave the bottom end a smoother, even more controlled feel out of corners. This isn’t a slower feeling (out of corners) by any means, but with the FMF muffler system installed the rear wheel feels better connected to the ground. There is more traction to the rear wheel out of hard pack corners when you roll on the throttle. Mid range pull surprisingly is better than stock as second and third gears can be stretched out slightly further down straights. The stock Yamaha engine character with the stock muffler has no problems carrying third gear around most corners and the same goes for the FMF 4.1 Yamaha power character. But, as we rode the stock muffler system and the FMF 4.1 RCT system back to back on several occasions, we could carry third gear through very tight 180-degree corners with the FMF system. The stock muffler had a slightly tougher time to get the rpm’s back up (in third gear) and let you accelerate hard upon exiting. Mid and top end RPM response is improved over stock, as the Yamaha is quicker to react to your throttle hand. Top end and over-rev is slightly improved (not that you need more) and you can really feel the top end pulling power when the track is tilled up really deep. The stock system feels somewhat empty on top compared to the FMF system, where the 4.1 will still pull hard.