that's odd. i've been racing two stroke dirt bikes for over 40 years. back in the day i used avgas. never a problem. these days it's not easy to get so i get fuel from the speed shops and mix it (i don't wring it quite so hard these days).
40 years ago, 100 LL avgas was fairly new on the market and 80/87 avgas was plentiful. If you were running 80/87, it would have a lot less lead.