Occasional Misfire

1776 with twin Kadrons and 009. Fires up OK but starts misfiring down the road,then clears, then misses again and so on. Plugs, leads,cap,rotor,points,condensor,coil all new. Tappets set OK. When idling, Numbers 1&3 dont seem to be doing much when I remove the plug leads. Im baffled. Can anyone help Mart