What is the number of the spark plug used in this model?

Hi,
It is probably a CJ7Y/CJ6Y/RCJ6Y Champion number. One of the three if it requires a 3/4" socket to remove. If it requires a 5/8" socket, then it is likely a DJ7Y Champion plug.
Peace,
Clarke
PS That MPH rating as an identifier is worthless sinc you or I can blow that hard through a common straw. It is volume that counts.