Many motorcycles these days are with catalysts inside the mufflers, when unburned fuel enters the muffler and gathers in the honeycombs, it’ll be lit up by the exhaust gas and make the temperature rise rapidly. In case the temperature exceeds the maximum allowable temperature (1200℃), the metal honeycomb will get ablated, fell off, or melted.
To avoid such a problem, you should never operate the vehicle in ways that may cause unburned fuel to enter the muffler, such as hitting the accelerator at idle or coasting with the engine off. For motorcycles with multi-cylinder engines above 250cc, you should stop the vehicle immediately if you find one or more cylinders not working but no defect indication, in this case, the catalysts might get ablated after running for a short distance (250cc vehicle running for 4km with 1 cylinder working).
Always fill your gas at official gas stations, never fill gas into the muffler.
Currently, motorcycles are with catalysts diameter 200 or 300 meshes, which are smaller than the 100-mesh they used to be, thus they’re easier to get stuck. If there’re excessive impurities in the gas or fuel enters the muffler, the catalysts will get stuck. Therefore, please always fill your gas at official gas stations, and never fill gas into the muffler.
heat dissipation on the surface.
Black painting on the muffler surface usually turns lighter or even turns grey under high temperature. To avoid color change, you have to make sure no burning inside the muffler and good heat dissipation on the surface. These are the measures to take: Do not run the vehicle for long with the choke valve shut; do not hit the accelerator at idle for long, do not add windshield or other decoration in front of the engine and muffler; do not run the vehicle at low gear for long and/or with a heavy load.
Besides, paint ingredients may change under high temperatures, and some micro holes may be generated. Some ingredients in the dirt such as SiO2 may enter these holes and merge with the paint by heat, making it hard to clean. To avoid such problem, you should clean the muffler when there’re many stains like oil, dirt on the surface.