Do you have a year, hp, and model number. Post a picture of the motor and a pic of the rope sheave or any location on the motor that has a serial or model number.
Lots of Champion models. Need to know which one. Some use Phelon or Scintilla coils (like Mercury. Some have metal centrifugal impellers, some have rubber.
I have a Champion Majestic and used standard OMC coils, but I had to remove them from the laminations and install them on the Majestic coil laminations.
The model number is often stamped into the side of the transom clamp assembly and may be painted over but still legible. It will likely be a number and a letter, like 1J, 1K, 4K, etc, but some have more characters, like the Hydrodrive units where model may be a format like 4LHD. Like Frank said, some never need an impeller if it is aluminum.
Dave