What octane fuel are you running?

I run a 72 340 with 10:5 to 1's on 87 octane ran awesome till the new gas with ethanol came around...the afb would not restart when hot....hold her to the floor until it started.....switched to holley and 2" spacer changed timing......awesome only had spark knock after sitting in traffic till it was runnin 205 with the boat hooked to the back of it.....was 100* plus that day