Out here in North California where we have 80/87 and 100LL the difference is that 80/87 typically has .5ml of lead and the 100LL has a max of 1.9 ml. lead. However some of the 100LL has far less than the max and according to the big engine shops doesn't provide enough lead during the breakin period. On the Stromberg carb. not going over 5000 feet something is wrong with it. Mine and most other properly maintained coupes had the carb wired full rich after a thorough cleaning and has routinely operated perhaps 1000 hours in
the 5-12,000 feet range with little leading problems like some of you are describing. It has been to 14,450 feet overlooking Mt. Shasta so if yours doesn't work at altitude with or without leaning there's something wrong with it. I would have to suspect the biggest lead problem to be improper operation at reduced throttle levels. You will experience more leading, at least I did at reduced throttle settings until the prop was pitched to 7148 on the C-85 and it now turns 2550 in like it's supposed to. Yes it burns more fuel but does cruise faster and has no leading problems. The plugs I pull daily from customers that are leaded up are flown slow and at only low altitudes and also have infrequent oil changes. Yes by all means if you must run auto fuel do cut it with 100LL not just 80/87 as some lead is needed for proper seat conditioning./tom
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