He left Cairo along the Nile River on 14 January 1705 - with seven companions that Father Giuseppe da Gerusalemme was leading - in order to go to Ethiopia to begin their mission. In June the team arrived in Debba in Sudan but were unable to continue due to tensions and so on 21 August took refuge in Allefun. The team remained there until being called to Sennar on 31 March 1708 but over time some of the members died or returned home which left Weiss alone with Giuseppe and with Michele Pio Fasoli. But there was a setback upon Giuseppe's death in May 1709 which later forced Weiss and Fasoli to return to Cairo on 30 June 1710. On 20 April 1711 the officials of Propaganda Fide in Rome asked the two to attempt to travel to Ethiopia once more prompting their departure on 3 November 1711 alongside Antonio Francesco Marzorati; the trio arrived in Gondar on 20 July 1912 to have the emperor Yostos receive them.
