Make sure the plugs are connected the right way, (in the correct firing order) If you muddle them up somtimes it will run but only on 2/3 cylinders!! Pops and backfired are a common give away.
Check that first because i have done it many times!
It will be somthing like 1-3-4-2 So find out where number 1 is on the dizzy cap and ensure the ones that follow it connect as shown.
On the distributor Spark plugs
Plug1 ---> Cylinder 1
Plug2 ---> Cylinder 3
Plug3 ---> Cylinder 4
Plug4 ---> Cylinder 2
Sorry if you already knew that, best to make it clear the first tiem just incase you dont know about the firing order

By the way, if you look down on the top of your distributor, number 1, is TOP RIGHT
2 1
O
4 3
Like that ^^^
And if that doesnt work, you need a compression test
