There are several aftermarket muffler sillencers out there that attach to the factory exhaust. Does anyone know if they cause damage or decrease performance on the ATV???

 

Damage...only if you neglect to rejet! Without a rejet it will be lean, but not necessarily run bad, which can be deceiving. Lean means hot, and a burned up engine!

Most all the aftermarket mufflers will improve performance over a stock one. It is a good idea to open up the air intake at the same time.

 

Thanks for the response RECONRANGER.

I forgot to mention that my ATV is a 4 stroke (2007 Big Bear-Yamaha) and that the silencer attaches to the end of the existing stock muffler.

Is the rejet still an issue???? I assume the dealer can do this ??
I know my way around a car engine but I'm new to the ATV scene.

 

I haven't dealt with 100's of bike or anything,,,, but everytime I decrease backpressure (ie removing a muffler or aftermarket exhaust) I end up with a black spark plug. And everytime I remove an air filter or add a KN filter I get a lean white looking plug. Maybe I live in bizarro world or something, but that's what happens around here.

I always figure it like this: Removing backpressure "should" increase vacuum at the carb. Removing the air box lid "should" decrease vacuum at the carb. What your carb does with that change in vacuum is a function of the resistences of air flow and gas flow at each particular throttle position.