valve life was extended by the looser clearances.
Lean fuel mixtures will also shorten valve life or, in extreme cases,
burn holes in pistons. Reading spark plugs can be an indicator of
mixture. If in doubt, go to a shop with an infra-red exhaust analyzer to
determine an improper fuel mixture.
The author, John L. Bellah, is a member of SAE International. He
spent several years in the automotive tune-up field and is
thoroughly familiar with tune-up and carburetion issues on
vehicles from the 1940s through the 1970s.