Try replacing your condensor on the side of the dizzy. This can do the same thing and gets to the point where the car bunny hops and misses and has no power what soever.
This happened to me yesterday on the way home from work, put a new condensor on it and she's good as new, no missing or nothing.

hi I have been having a problem were my A12 engine misfires only under load never at idle it more noticeable when yo get to 4000rpm it will misfire a few time.

I had this problem a few weeks ago so I reset the point dwell to around 50 degrees before this it would misfire really bad problem seemed to had gone but has reappeared.

i rechecked the plugs and points and all seems good I also tried a different (original) coil and does same thing.

Any ideas?

Thanks!