When I disengag'd myself as above-mentioned from private Business, I flatter'd myself that, by the sufficient tho' moderate Fortune I had acquir'd, I had secur'd Leisure during the rest of my Life, for Philosophical Studies and Amusements (3.49)
By this point in the text, Franklin has worked hard and made enough money to retire. Good for him. It's what he wants to do with it that's really interesting. Instead of investing, or going on vacation, Franklin wants to invent more stuff and participate in philosophical debates. You know, as we all do. Unfortunately for Franklin, he's too good at political and diplomatic stuff, and instead of getting to spend his time inventing who knows what else, he ends up serving as a diplomat (this isn't fully covered in the Autobiography, but we're giving you the heads up anyway).