Cookie,
Interesting post, had the same issue with my GT6 engine in my MGB GT. Had knocked the timing back to 7 Deg BTDC, and it would pink on e10 and e5. So decided to set the timing the old way, at tick over, and advance to max RPM, then back off a little. Took it for a spin and couldn`t make it pink. Checked the timing with a strobe and its at 17 Deg BTDC.๐ค And no there is no rubber slippage on the pulley, timing marks were checked 3000 miles ago during complete rebuild, and checked again when I advanced the timing just recently. Sure there`s another 10 BHP on tap as well, and it runs happily on e10. I know this defies all logic, but think it could be down to the way modern fuel burn??? Mac.