All you did was install another carb and the timing changed?

You could have moved your distributor when installing the carb.

Did you check all of your plug wires for a good connection and that they are not being pinched somewhere.

Did you check the distributor cap to be sure that it is setting correctly on the distributor?

Do you have all of the vacuum lines connected and none of them are cracked & sucking air.

I bought a 52 Chevy PU that had a 283 in it. The complaint from the guy that I bought it from is that it had a miss and that he could not find and it of course was sluggish. He had been fighting with this for over 3 months and was tired of messing with it.

I drove it home and when I went to get out (with it running) I touched the door and got shocked. The guy had 1 plug wire that was too long and it was routed (had moved) between the frame and the inner finder well. You know what that does.

I drove it back the next day because he did not have the pink slip with him when I bought it (he worked with my brother-in-law). I told him what it was and offered to sell it back to him for the same as I bought it for. He said "no" a deal is a deal.