Cheech, if your motor doesnt cut smartly then the throttle barrel is fully closed, then you need to do this. If the motor is out of the plane, it may be easier to just do it anyway and save yourself future hassles.

On the muffler side, I did not use the paper gasket supplied, they always compress after a while and blow through or cause the muffler to fall off! Just a thin smear of RTV sealant is all thats required.