318 Engine stumble

The carburetor secondary butterflies should be adjusted so that the transition slots are perfectly square. If you have any questions about that, there are many videos on youtube to show how.

Also, it sounds like you could use more initial timing. Try it on 12. If it does not spark knock on acceleration, try 14, then 16........keep going up as long as it does not spark knock. If you find where it spark knocks, back off till it quits and lock er down.