There are many myths about nitro fuel, and there are also many facts which are strange enough to sound like myths.

  1. You need to re-break-in an engine after switching fuels.
    No, you don't. After breaking in an engine, it cannot be broken in again, it can only be worn out. Attempting to break it in again will only waste fuel and time. However, you will have to tune the engine again, and it can be helpful to reset the carburetor settings to the original factory specifications before doing this.
  2. You must always use the exact same fuel in your engine as it was broken in with.
    No, but it can be helpful to avoid switching fuels. The engine essentially does not care what is in it, as long as it will burn. But, different oil and nitro percentages will make the engine run at slightly different temperatures, which can cause extra wear on the engine. It's a good idea not to experiment with fuels, but switching because the brand you were using is no longer available, etc, is perfectly acceptable.
  3. You must always use a head shim and a colder glow plug when running higher nitro fuels.
    This is based on truth, but is told as an absolute requirement. Some engines are already configured for higher nitro fuels from the factory, and some others run fine without any changes. A colder glow plug often runs better, while an extra head shim will lower the compression and prevent any detonation from occuring. Check your engine manual!
  4. Nitro fuel is a good cleaner for foam R/C air filters.
    This is actually true, as weird as it sounds. The fuel will expand the foam and help the dirt come out, and it actually cleans slightly better than soapy water. This will leave an oily residue in the filter after it dries, but the filters should still be oiled with an air filter oil. Some people even prefer to wash it out with soapy water before oiling. And please make sure you do this safely; do it outside and where the wind will not blow the fumes in your face.