Ok, looks like it was the idk adjustment screws on the carb. I don't think I've ever had a carb that needed the idle adjustment screws so far out! Maybe it's be because the 750 carb is too big for my 318.

I've got it down to 14 btdc at 970rpm with 23 inches of vacuum. Gonna see if I can get it down to 800rpm and 12btdc