What type ignition? Points? If so, what are they set at? Double check the firing order of the plug wires. Make sure dist rotor points to number 1 plug wire when 1 is at TDC. Easiest way to do this is watch the rotor while you hold your thumb over the number one spark plug hole while someone cranks the engine over. See where the rotor points when your thumb feels the pressure against it (or gets blown off the hole).
Sounds like the firing order may be off, or points not adjusted correctly. Or both.
