I have a KZ440 that is running but not perfectly. It's starting a bit rough, but after it warms up is holding idle at around 800-1000rpm. When I rev it, there is a small lag and stutter, but not too bad. My issue right now is that there seems to be a lot of back firing and exhaust noise, which I think might be associated with the rusted muffler. The muffler body is in good shape (no exterior holes) except for the exit hole. It's a stock muffler, so has a 1"(or about that) exit hole, but has rusted out around this from exhaust moisture. I'm guessing that this is reducing the back pressure on the system and maybe leading to some of the roughness. That's my first question: do you think I'm right about this?
My second question is what to do. right now I want to get it running and use it for a bit to see if it's a bike I want to put time/$ into, so I'm not into restoring it right now. I'm wondering if I could clean up the soft rust, use a rust stabilizer to hold together the remaining muffler end and then use JB weld or epoxy putty to rebuild the rusted out portion. Any better ideas or objections?
so, I'm inferring that what you suggest is that I should replace the muffler completely. The stock muffler is welded, so I'd need to cut it above the weld and use a slip on, right? Any good resources for a new exhaust system? there really isn't too much rust on the pipes, but I'm sure there's some corrosion inside them.
Well, I cleaned up the flaking rust, cleaned it with HCl acid and washed it, then put on a JB weld patch. It's working great. Hardened rock hard in about 15 minutes with the pipe warm and I've since started sanding it so it doesn't look so much like I stuck a bunch of gum on the muffler. It should work for a few months, which will be plenty of time for me to figure out if the rest of the bike is worth putting the cash into. Sorry I don't have a before picture, but you get the idea. It's definitely a lot more quiet and it really seems like the throttle response is a lot better; less lugging before revving up.