A little Marvel Mystery oil in the tank at fillup if its going to sit much. Definitely use premium no-alcohol gas if it is available in your area, it is here and I won't run anything else.
I run Marvel Mystery Oil and a splash of generic lead substitute. All three of my A's seem to be happy thus far.
From past experiences - I use Marvel Mystery Oil to all of my mechanical machinery. I add 3 or 4 oz. to my full tank of gas in my "A", add a bit to my pressure washer, generator, lawn mower, etc. and if I remember....we (my wife and I) add a couple of ounces to our Harley Davidsons. It seems to keep fuel machinery from deteriorating and helps to keep fuel from varnishing-up from long storage times.
What about Morey's upper cylinder lubricant? Not sure if MMO is available here in New Zealand
Snake oil.
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It says roughly: In 1927 approx. 14%of cars were high compression (5 to 1 or higher). By 1928 it was 56%. 1929 77%. Don't think Henry believed in lead.