Start with the basics - timing/dizzy (points/condensor pitted or shagged) module got the right heat sink paste under it, basic condition of cap/rotor/leads, fuel - does it idle properly or is there fuel pouring down the primaries at idle a has the carby been off it recently as some folks aren't to clued up on both installing the float or setting its level, is the fuel much older than a couple of months, does it have a vac leak base of the carby sucking air, is the manifold tight, vac tree or hose leaking?

Something there should point towards the issue. I'm suspecting fuel itself if it has been a while since you last filled it.