My 1977 CB400F original 39 year old muffler is in very poor shape, appearance wise, and the baffle had rotted away into many pieces so I bought a MAC muffler for the bike last fall. I have never been happy with the sound the MAC produced and the engine felt choked by the goofy baffle setup in the MAC. I'd like to find a good original muffler but I am NOT paying the ridiculous price I have seen them going for and I don't have any confidence in the aftermarket replicas so it's the MAC for now.
I pulled the MAC baffle out and modified it to be a straight thru pipe. I have no access to a welder at the moment so I just squared the ends after straightening the deformed pipe to be the same diameter as the other pipe. Aluminum sheet and some SS hose clamps attach it all together. Temporary fix until my welder shows up. The clamp actually works good and because it is clamping a straight pipe with no baffle holes it might last a long time.
Sounds much freer but slightly on the loud side. The engine has pods and has been rejetted with one step bigger mains, repositioned needle clip, different pilots and was running very slightly rich with the stock MAC setup but now, after a plug chop, it is running near perfect when doing a full throttle plug chop. I still have a slight hesitation just off idle that did not change with the mod'ed baffle. The low and mid range is still slightly rich.
Here is a video of the bike with the mod'ed baffle. The camera is a GoPro 3 with an external lavalier mic attached to the belt loop at the small of my back so that the mic is about 24" higher and 6" forward of the exit of the muffler. For reference the speedo is 65 MPH with the needle straight up and the tach is 6K RPM straight up.
I thought people asking about MAC exhaust might get some info from this. My opinion of MAC stuff is that they make affordable stuff that is not of the highest quality but it does function OK. The MAC baffle setup for this muffler is poorly thought out but easily modified in many different ways. Getting the length of the baffle is important so that it seats and seals to the muffler body.
