Originally Posted by chasbmw
Wizbang spark plugs are to give extended service life in todays vehicles, think replacement @ 25-35kmiles rather than the normal 5k miles on our bikes.
Exactly, whizzbang plugs are meant for a engine with high efficiency I.E. a very tightly controlled combustion process. These old aircooled tractor motors (while very reliable) have too much variation in combustion chamber temps with minimal fuel control. Modern fuel injection has maps to match the fuel delivery rate precisely to internal temp, atmospheric temp, engine speed and load (and other stuff).
An old motor with carburetors will not keep the Wizzbang plugs clean enough to take advantage of the extended service intervals and the wizzbangs do very very very little, if nothing at all to promote combustion efficiency. You would not put iridium plugs in a 1972 Ford with a 300 6cyl and expect them to last 80k-90-100k miles even if the motor was fresh.
On these antique motors save yourself some money, buy a quality "normal" plug and inspect them at the correct intervals.