Did Carl lose some of his motivation after 1973?

[Lonely Summer]

Carl went through some tough times family wise in the mid Seventies, and wore out after carrying the group production wise for 6 years, just as Brian did (also 6 years). In the interest of family privacy, I don't want to say more.

I don't think it's any secret here that Carl battled drugs in the mid 70's; in later years, much of his energy was directed at ending the Brian/Landy relationship. That took a lot out of him. Carl always had to be the responsible brother, the adult in the group.