TOPIC:

I have a 78 kz400 with dual exhaust off a 75 parts bike. I recently got it running and took it on a long ride with a group of friends. I lost power and it had a bad knock so I'm in the market for a new engine!
Other than that I love my kz, it's my first bike and I'll never sell it.

Welcome aboard.

Have you considered diagnosing and repair rather than replacement? Any replacement engine you get will be just as old, and may be in no better shape.