I am a boating newbie and the new owner of a 1970-something Johnson 40hp
outboard. I have had it out for maybe 8 hours so far without any problems.
The other day it started acting up. When I push the throttle forward, the
boat moves, but then the engine just rev's up and the boat doesn't go
anywhere. The closest comparison I can make is that it seems like a clutch
is slipping.

I'd like to repair the engine myself. Where should I start looking?

Thanks for any info,

Pyro Dave.