Does it just smell rich or are the plugs dark brown to black , a long duration cam will make any engine seem rich at idle & Edelbrock carbs are always set too lean , the stumble could be in th eaccerater pump as suggested or it could be in the timing , you need approx 12-16 * at idle & 36* total advance , I suggest either disconnecting the vacuum advance or severly limiting it using an allen wrench in the hole the vacuum line connects onto & turning it most of the way out counterclockwise , this may take care of the stumble alone